Huperzine A is a Chinese herb extract used for Alzheimer’s disease. We conducted this review to evaluate the beneficial and harmful effect of Huperzine A for treatment of Alzheimer’s disease.
We searched for randomized clinical trials (RCTs) of Huperzine A for Alzheimer’s disease in PubMed, Cochrane Library, and four major Chinese electronic databases from their inception to June 2013. We performed meta-analyses using RevMan 5.1 software. (Protocol ID: CRD42012003249)
20 RCTs including 1823 participants were included. The methodological quality of most included trials had a high risk of bias. Compared with placebo, Huperzine A showed a significant beneficial effect on the improvement of cognitive function as measured by Mini-Mental State Examination (MMSE) at 8 weeks, 12 weeks and 16 weeks, and by Hastgawa Dementia Scale (HDS) and Wechsler Memory Scale (WMS) at 8 weeks and 12 weeks. Activities of daily living favored Huperzine A as measured by Activities of Daily Living Scale (ADL) at 6 weeks, 12 weeks and 16 weeks. One trial found Huperzine A improved global clinical assessment as measured by Clinical Dementia Rating Scale (CDR). One trial demonstrated no significant change in cognitive function as measured by Alzheimer’s disease Assessment Scale-Cognitive Subscale (ADAS-Cog) and activity of daily living as measured by Alzheimer’s disease Cooperative Study Activities of Daily Living Inventory (ADCS-ADL) in Huperzine A group. Trials comparing Huperzine A with no treatment, psychotherapy and conventional medicine demonstrated similar findings. No trial evaluated quality of life. No trial reported severe adverse events of Huperzine A.
Huperzine A appears to have beneficial effects on improvement of cognitive function, daily living activity, and global clinical assessment in participants with Alzheimer’s disease. However, the findings should be interpreted with caution due to the poor methodological quality of the included trials.
Citation: Yang G, Wang Y, Tian J, Liu J-P (2013) Huperzine A for Alzheimer’s Disease: A Systematic Review and Meta-Analysis of Randomized Clinical Trials. PLoS ONE 8(9): e74916. https://doi.org/10.1371/journal.pone.0074916
Editor: Roberta W. Scherer, Johns Hopkins Bloomberg School of Public Health, United States of America
Received: March 26, 2013; Accepted: August 7, 2013; Published: September 23, 2013
Copyright: © 2013 Yang et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This review was funded by the Program for Innovative Research Teams of Beijing University of Chinese Medicine (2011-CXTD-09 and -21). Prof Jinzhou Tian and Jian-Ping Liu were supported by the grant the 111 Project (No.B08006), and the Technological Platform of Clinical Evaluation and Research for New Herbal Medicinal Products (2011ZX09302-006-01). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors declare that they have no known conflicts of interest.
Alzheimer’s disease (AD), first described by German psychiatrist Alois Alzheimer in 1906, is a progressive neurodegenerative disease characterized by cognitive deterioration together with behavioral disturbances and declining activities of daily living . It is the leading cause of dementia, resulting in nearly 70% of dementia worldwide by 2005 . An estimated 36 million people  worldwide are living with dementia today and more than 115 million is predicted for the year 2050 .
Current medications can not cure AD but may help lessen or stabilizes symptoms of AD for a limited time. There are five prescription drugs approved by the U.S. Food and Drug Administration (FDA)-donepezil, galantamine, rivastigmine, tacrine and memantine to treat its symptoms . The first four drugs are cholinesterase inhibitors, which can prevent the breakdown of acetylcholine involved in memory, judgment and other thought progress. Memantine appears to work by regulate the activity of a different chemical messenger in the brain. However, these drugs have some common side effects including nausea, vomiting, loss of appetite and increased frequency of bowel movements, and tacrine is rarely prescribed today because of possible liver damage . Therefore, promising new treatments to slow or stop the progress of AD are urgently needed.
Huperzine A, derived from the Chinese herb Huperzia serrata, was identified by scientists in China in the 1980s as a potent, reversible, selective inhibitor of acetylcholinesterase (AChE) , which has a mechanism of action similar to donepezil, rivastigmine and galantamine. A large number of preclinical studies and clinical trials had shown the potential effect of Huperzine A in treating AD. A Cochrane systematic review published in 2008 involving 6 randomized trials with 454 AD participants suggested that Huperzine A seemed to have some beneficial effects on AD, however, due to poor methodological quality and small sample size there was still insufficient evidence for clinical recommendation . Another systematic review evaluating single Chinese herbs for AD involving only English-language trials shared similar inconclusive findings .
More recently, a variety of clinical trials assessing the efficacy and safety of Huperzine A in treating AD became available. Therefore, we conducted a systematic review to evaluate the beneficial and harmful effect of Huperzine A for treatment of Alzheimer’s disease.
Materials and Methods
The supporting PRISMA checklist is available as supporting information; see Text S1.
Standard protocol registrations
This systematic review was registered in PROSPERO, an international prospective register of systematic reviews. The registration identifier of the protocol is CRD42012003249 .
Search strategy and study selection
Two authors (GYY and YYW) searched the following electronic databases from their inception until June 2013: PubMed, Cochrane Dementia and Cognitive Improvement Group and Cochrane Central Register of Controlled Trials (CENTRAL) in the Cochrane Library (April, 2013), China Network Knowledge Infrastructure (CNKI), Chinese Scientific Journals Database (VIP), Wan Fang Database and Sino-Med Database.
We also searched for ongoing trials from mainstream registries: The metaRegister of Controlled Trials , ClinicalTrials.gov trials registry , The Australian New Zealand Clinical Trials Registry , The World Health Organization International Clinical Trials Registry platform , and CentreWatch .
We also searched unpublished postgraduate theses in Chinese databases. The reference lists of all relevant papers found electronically were hand-searched.
The English searching terms were used individually or combined including “huperzine A”, “Alzheimer’s disease”, “AD”, “Alzheimer disease”, “randomized controlled trial”, “controlled clinical trial”, “randomly”, “trial”, “randomised” and “randomized”. The Chinese searching terms were used individually or combined including those for the generic name of Huperzine A (“Shi_shan_jian-jia”), trade names for Huperzine A (“shuang_yi_ping”, “ha_bo_yin”, “nuo su lin”, “yi nuo”, “fu_bo_xin”, or “rui li su”), Alzheimer’s disease (“lao_nian_chi_dai”, or “a_er_zi_hai_mo”), and randomized (“sui_ji”). No language restriction was applied. The detailed search strategy of each database is available as supporting information; see Search strategy S2.
Two authors (GYY and YYW) identified studies that met the inclusion criteria and extracted data independently. The extracted information included: study population, participant demographics and baseline characteristics; details of the intervention and control conditions; study methodology; outcome measures and main results. Any discrepancies were identified and resolved through discussion with a third author (JPL) where necessary.
Inclusion and exclusion criteria
- Type of study. We included parallel group, randomized control trials to assess the beneficial effects and harms of Huperzine A for treating Alzheimer’s disease, regardless of blinding or publication types. Cross-over randomized trials were also included, but only the outcomes from the first period of treatment were extracted and analyzed. Quasi-randomized trials were excluded.
- Type of Participants. Participants with Alzheimer’s disease regardless of the disease course and severity and diagnosed with any one of the following criteria:
- The International Classification of Disease (ICD) version 9 or 10;
- The Diagnostic and Statistical Manual of Mental Disorder (DSM) III, III-R or IV;
- The National Institute of Neurological and communicative Disorder and Stroke-Alzheimer’s Disease and Related Disorder Association (NINCDS/ADRDA).
- Type of interventions. Huperzine A for participants with Alzheimer’s disease, regardless of manufactures, preparation form, dose, and duration.
- Type of control. Placebo, no treatment, conventional intervention. We also allowed a Co-intervention if applied in all arms.
- Type of outcome measures. The primary outcomes were cognitive function, and quality of life (QoL) measured by validated instrument. The secondary outcomes were activities of daily living (ADL), global clinical assessment, and adverse effects of Huperzine A.
Risk of bias (methodological quality) assessment
Two authors (GYY and YYW) independently assessed the risk of bias using the Cochrane of risk of bias tool . The following items were assessed:
- Random sequence generation (selection bias)
- Allocation concealment (selection bias)
- Blinding (performance bias and detection bias)
- Incomplete outcome data (attrition bias)
- Selective outcome reporting (reporting bias)
- Other bias
The risk of bias was categorized as low/unclear/high risk of bias. Trials which met all criteria were judged as having a low risk of bias, trials which met none of the criteria were judged as having a high risk of bias, and trials with insufficient information to judge were classified as unclear risk of bias. Disagreements between the review authors over the risk of bias in specific studies were resolved by discussion and consensus, with involvement of a third review author where necessary.
Strategy for data synthesis
We performed meta-analyses using RevMan 5.1 software. We summarized data using risk ratios (RR) with 95% confidence intervals (CI) for binary outcomes or mean difference (MD) with 95% CI for continuous outcomes. If different measurement scales were used, standardized mean difference (SMD) analyses were performed. For cross-over trials, only the outcomes from the first period were included. If required data were not reported, we requested data from corresponding author. We used fixed effects model unless there was evidence of heterogeneity. We assessed heterogeneity using both the Chi-squared test and the I-squared statistic. We considered an I-squared value greater than 25% indicative of substantial heterogeneity. We performed funnel plots to detect publication bias.
Description of studies
A flow chart showed the search process and study selection (Figure 1). We included 20 RCTs – for this systematic review, including five three-armed RCTs , , , ,  and one five-armed RCT . All RCTs were conducted in China, except one which was conducted in the United States , and all were published in full: 18 trials – were published in Chinese and two were published in English –.
Presentation of the procedure of literature searching and selection with numbers of articles at each stage.
One ongoing registered RCTs was identified from www.clinicaltrials.gov: NCT01282619 evaluating the safety and efficacy of Huperzine A sustained release tablets in patients with mild to moderate Alzheimer’s disease. However, the status was unclear and data were not available.
Table S1 listed the detailed characteristics of the included trials. The 20 RCTs involved 1823 participants with Alzhermer’s disease, aged between 50 to 85 years old. The duration of treatment varied from 8 weeks to 36 weeks, with an average duration of 14.7 weeks. The dosage of Huperzine A varied from 0.2mg to 0.8 mg daily, with an average dose of about 0.37 mg daily.
There are various comparisons: Huperzine A versus placebo (10 trials –, 50%), Huperzine A versus no treatment (2 trials –, 10%), Huperzine A versus psychotherapy (1 trial , 5%), Huperzine A versus conventional medicine (6 trials –, 30%), and Huperzine A plus Chinese herbal medicine versus Chinese herbal medicine alone (1 trials , 5%).
Risk of bias assessment
For random sequence generation, four of the 20 trials (20%) , , ,  used a random number table, one trial (4.17%) used drawing lots, and the other 15 trials (75%) just simply mentioned “randomization” and did not report the specific method of random sequence generation.
For allocation concealment, one trial (5%)  used a center controlled method, while the other 19 trials (95%) did not report information on this. One trial , though not reporting the method of allocation concealment, assessed the effectiveness of allocation concealment at the end of study by querying clinician, psychometrist, study partner and coordinator. So we judged it as low risk for this item.
For blinding, seven trials (35%) used double-blinding method by blinding of participants and researchers, four trials (16.67%) used single-blinding method in which three reported blinding of outcome assessment and one trial just mentioned “single-blinding”, and the other nine trials (45%) did not give information on blinding.
For incomplete outcome data, four trials (20%) , , ,  reported the detailed information of attrition by describing the number and reasons for withdrawal, of which three , ,  used intention-to-treat analysis. The remaining trials did not report the information of attrition. Though the number of participants in randomization and in data analysis was equal, it is still unclear whether there is incomplete outcome data in those trials.
For selective outcome reporting, only one trial (5%)  was at low risk. This trial gave the clinical trial identifier number, and we were able to find the protocol for comparison and assessment. Since the other 19 trials (95%) did not report the information of registration, we could not make a comparison between the protocols and trial reports.
In conclusion, after assessing the selection bias, performance bias, detection bias, attrition bias and reporting bias of the 20 included trials, we found the general methodological quality of most trials was moderate or poor. (Figure 2, 3)
Presentation of the risk of bias summary of the review author’s judgments about each risk of bias item for each included study.
Effects of interventions
The effect estimates of Huperzine A were shown in the Table S2. We failed to use intention-to-treat analysis, because most included trials did not report the participant flow, especially the number of losses or exclusions after randomization together with reasons.
1. Cognitive function.
Compared with placebo, four meta-analyses and most individual trials reporting the last observation scores of cognitive function favored Huperzine A: seven trials favored Huperzine A as measured by Mini-Mental State Examination (MMSE) at 8 weeks , , , 12 weeks , , , and 16 weeks , but not at 24 weeks ; four trials favored Huperzine A as measured by Hastgawa’s Dementia Scale (HDS) at 8 weeks , ,  and 12 weeks ; four trials favored Huperzine A as measured by Wechsler Memory Scale (WMS) at 8 weeks , ,  and 12 weeks . In trials reporting the change in scores from baseline, when measured by MMSE, three trials showed similar findings favoring Huperzine A at 12 weeks , , 16 weeks , 24 weeks  and 36 weeks ; however, when measured by Alzheimer’s Disease Assessment Scale-Cognitive Subscale (ADAS-Cog), two individual trials demonstrated there were no statistical differences between Huperzine A and placebo , .
Compared with no treatment, one trial  reporting last observation scores favored Huperzine A as measured by MMSE at 12 weeks, and another trial  reporting the change in scores from baseline also favored Huperzine A as measured by WMS.
Compared with psychotherapy, one trial  reporting the change in scores from baseline favored Huperzine A when measured by MMSE at 12 weeks.
Compared with conventional medicine, one meta-analyses and all individual trials reporting the last observation scores of cognitive function after treatment favored Huperzine A or demonstrated no statistical difference between groups: as measured by MMSE, Huperzine A resulted in higher scores compared with Piracetam at 8 weeks –, but there were no statistical differences between Huperzine A and Galanthamine hydrobromide , Vitamin C  or Donepezil ; as measured by HDS, one trial  showed no difference between Huperzine A and Galanthamine hydrobromide at 8 weeks; as measured by WMS, Huerzine A was superior compared with Piracetam at 8 weeks  and was not statistically different from Galanthamine hydrobromide at 8 weeks .
One trial  comparing Huperzine A plus Chinese herbal medicine versus Chinese herbal medicine alone showed no statistical difference between two groups as measured by MMSE at 8 weeks and 12 weeks.
The forest plots of comparison of Huperzine A versus placebo for the outcome of cognitive function as measured by MMSE and activities of daily living as measured by ADL in trials reporting the last observation scores are shown in Figure S1 and Figure S2, respectively.
3. Activities of daily living.
Compared with placebo, two meta-analyses and most individual trials reporting the last observation scores favored Huperzine A: seven trials favored Huperzine A as measured by Activities of Daily Living Scale (ADL) at 6 weeks , , 12 weeks , , and 16 weeks , but not 8 weeks  and 24 weeks . In trials reporting the change in scores from baseline, when measured by Alzheimer’s Disease Cooperative Study Activities of Daily Living Inventory (ADCS-ADL), one trial  showed no significant change in activities of daily living in Huperzine A group at 16 weeks; however, when measured by ADL, three trials favored Huperzine A at 6 weeks , 16 weeks , 24 weeks  and 36 weeks , but not at 12 weeks , .
No trials comparing Huperzine A versus no treatment reported this outcome.
Compared with psychotherapy, one trial  reporting the change in scores from baseline favored Huperzine A as measured by ADL at 12 weeks.
Compared with conventional medicine, three trials reported the last observation scores after treatment on this outcome. One trial  demonstrated Huperzine A had a better effect than Piracetam at 8 weeks, but two individual trials showed there were no statistical differences between Huperzine A and Galanthamine hydrobromide , or Huperzine A and Donepezil .
One trial  comparing Huperzine A plus Chinese herbal medicine versus Chinese herbal medicine alone showed no statistical difference between the two groups as measured by ADL at 8 weeks and 12 weeks.
4. Global clinical assessment.
One trial  reporting the last observation scores demonstrated Huperzine A had a better effect than placebo for the global clinical assessment as measured by Clinical Dementia Rating Scale (CDR) at 16 weeks. No other trials in other comparisons reported this outcome.
A Summary of Finding table presented the main findings of Huperzine A versus placebo for Alzheimer’s disease, and provided key information about the quality of evidence, and a summary of important statistical results on cognitive function, quality of life, activities of daily living and global clinical assessment (Table 1).
5. Adverse events.
Of the 20 trials, 7 trials (35%) did not report information on adverse events, one trial (5%) reported no adverse events, and the remaining 12 trials (60%) described the adverse events in detail. The adverse events were mild and included nausea (7/20, 35%), anorexia (loss of appetite) (5/20, 25%), dizziness (4/20, 20%), vomiting (4/20, 20%), constipation (3/20, 15%), insomnia (3/20, 15%), excitability (2/20, 10%), thirst (2/20, 10%), sweating (2/20, 10%), bradycardia (2/20, 10%), abdominal pain (2/20, 10%), somnolence (1/20, 5%), hyperactivity (1/20, 5%), nasal obstruction (1/20, 5%), diarrhea (1/20, 5%), and edema (1/20, 5%).
All of the 13 trials reporting adverse events stated that there were no statistically significant differences between groups on the incidence of adverse events. No trial reported severe adverse events possibly related to Huperzine A.
One trial  reported Huperzine A was generally well-tolerated at doses of up to 0.4 mg BID for 24 weeks, even in subjects unable to take other cholinesterase inhibitors.
We conducted funnel plots to detect the publication bias (Figure S3). It demonstrated asymmetrical funnel plots, suggesting potential publication bias.
In this review, we found compared with placebo, Huperzine A demonstrated a potential beneficial effect for Alzheimer’s disease on the improvement of cognitive function as measured by MMSE, HDS and WMS, activities of daily living as measured by ADL and the global clinical assessment as measured by CDR, which is in accordance with the Cochrane reviews published in 2008 ; when compared with no treatment, psychotherapy and conventional medicine, the findings also favored Huperzine A.
The 2008 Cochrane review included 6 RCTs comparing Huperzine A with placebo to assess Huperzine A for AD, but reported inconclusive results due to the small sample size and limited methodological quality. Though our review included 10 placebo controlled RCTs (including the six trials included in the 2008 Cochrane systematic review) and another 10 RCTs with other comparisons, we still could not make firm conclusions due to the different measurements (scales) of each outcome, various duration of treatment, and diverse reporting methods in included trials, which resulted in few trials or only one trial in each subgroup. In addition, the methodological quality of most trials was classified as moderate or low, except one phase II trial  conducted in United States and published in English.
The following problems in reporting contribute to the limited methodological quality of most included trials: (1) methods of random sequence generation and allocation concealment were not reported; (2) blinding was unclear, if not, who was blinded was unclear; (3) withdrawal/dropout during the trial and use of intention-to-treat analysis was unclear and, if reported, the detailed reasons of withdrawal/dropout were not reported; (4) information on registration was unclear. We highly recommend further randomized trials should report according to the CONSORT Statement . We also recommend further researchers assess allocation concealment and blinding at the end of study, which will be helpful to judge the implementation.
The funnel plot analysis showed asymmetry, which suggests the possibility of publication bias of Huperzine A for AD. The power of the test might be low to distinguish chance from real asymmetry, due to only eight trials included in the funnel plot. However, considering almost all the trials claimed a positive effect of Huperzine A, we still suspected there might be some ‘negative’ studies unpublished. Some researchers suggested prospective registration of clinical trials and/or publication of clinical trial protocol as a solution . In addition, our study might have a limitation of missing some trials since we did not search pertinent English databases such as AMED and EMBASE.
A systematic literature review  of 1902 articles identified 68 relevant AD scales. Most scales assessed cognition, activities of daily living and global changes, while other scales assessed behavior/Neuropsychology, participant’s quality of life, and communication/social interaction. In the current review, we also found there were several scales used to measure cognition, activities of daily living and global changes of Alzheimer’s disease in the included RCTs, but no trials reported participant’s quality of life and communication/social interaction, which is important for participants. The trial  conducted in the United States reported cognitive function measured by ADAS-Cog and activities of daily living measured by ADCS-ADL and found no beneficial treatment effect of Huperzine A, but did see a positive effect on cognitive function when measured by MMSE. Twenty trials used MMSE alone or in combination of HDS and WMS to measure cognitive function, with one trial  using ADAS-Cog and MMSE. We recommend using at least ADAS-Cog and MMSE to measure cognitive function in the future, to improve the reliability and validity.
Though none of the included trials reported severe adverse events possibly related to Huperzine A, we cannot draw firm conclusions about the safety of Huperzine A since seven trials did not report information on safety. The duration of treatment in most trials was 8 weeks or 12 weeks, so the potential beneficial or harmful effect of Huperzine A for treatment of AD might only result from symptomatic changes and short treatment duration, which is consistent with the findings of a previous review . The included trials used different doses of Huperzine A, varying from 0.2mg to 0.8 mg daily. One trial  reported Huperzine A was generally well-tolerated at doses of up to 0.4 mg BID for 24 weeks, even in subjects unable to take other cholinesterase inhibitors. Since most participants with Alzheimer’s disease require lifelong treatment, the long-term safety of the treatment is still an important concern. We recommend that further studies should pay attention to the monitoring and reporting of adverse events and long-term safety by designing a longer duration of treatment and a long-term follow-up.
Huperzine A seems to have some beneficial effects on improvement of cognitive function, daily living activity, and global clinical assessment in participants with Alzheimer’s disease. However, the findings should be interpreted with caution due to the poor methodological quality of the included trials. More rigorous trials are warranted to support its clinical use.
Forest plot of comparison of Huperzine A versus placebo for cognitive function measured by MMSE.
Funnel plot of comparison of Huperzine A versus placebo for activities of daily living measured by ADL.
Funnel plot of comparison of Huperzine A versus placebo for cognitive function measured by MMSE.
Characteristics of 20 included randomized trials on Huperzine A for Alzheimer’s disease. Presentation of the characteristics of 20 included randomized trials on Huperzine A for Alzheimer’s disease, including study ID, No. of participant, intervention, control, outcome measure and follow-up information.
Effect estimates of Huperzine A for Alzheimer’s disease. Presentation of the effect estimates of Huperzine A for the treatment of Alzheimer’s disease, including information about different comparisons under different outcomes.
PRISMA checklist. Presentation of the PRISMA checklist of this systematic review and meta-analysis.
Search strategy. Presentation of the detailed search strategy of each database.
We thank Yun Xia from Division of Scientific Research, Dongfang Hospital, Beijing University of Chinese Medicine for her constructive suggestion in data analysis. We also thank Research Associate Huijuan Cao from Centre for Evidence-based Chinese Medicine, Beijing University of Chinese Medicine for her suggestions in data synthesis and drafting the manuscript.
Conceived and designed the experiments: JPL JZT. Analyzed the data: GYY YYW. Wrote the paper: GYY.
- 1. Hanns H, Gabriele N (2003) The discovery of Alzheimer's disease. Dialogues Clin Neurosci 51: 101–108.
- 2. Christiane R, Carol B, Richard M (2011) Epidemiology of Alzheimer disease. Nat Rev Neurol 73: 137–152.
- 3. Alzhermer’s Disease International (2009) World Alzhermer Report: World Alzhermer Report 2009. Available: http://www.alz.co.uk/research/world-report. Accessed 28 January 2013.
- 4. Alzhermer’s Disease International (2012) World Alzhermer Report: World Alzhermer Report 2012. Available at: http://www.alz.co.uk/research/world-report. Accessed 28 January 2013.
- 5. Alzheimer's Association. FDA-Approved Treatment for Alzheimer’s. Available at: http://www.alz.org. Accessed 29 January 2013.
- 6. Wang YE, Yue DX, Tang XC (1986) Anti-Cholinesterase Activity of Huperzine-A. Acta Pharmacology Sinica 7: 110–113.
- 7. Li J, Wu HM, Zhou RL, Liu GJ, Dong BR (2008) Huperzine A for Alzheimer's disease. Cochrane Database of Systematic Reviews DOI: 10.1002/14651858. CD005592.pub2.
- 8. Li-Min F, Ju-Tzu L (2011) A systematic review of single Chinese herbs for Alzheimer’s disease treatment. Evid Based Complement and Alternat Med DOI: 10.1093/ecam/nep136.
- 9. Yang GY, Wang YY, Xia Y, Tian JZ, Liu JP (2012) Huperzine A preparation for Alzheimer’s disease: a systematic review and meta-analysis of randomized clinical trials. PROSPERO: CRD42012003249. Available: http://www.crd.york.ac.uk/PROSPERO/display_record.asp?ID=CRD42012003249. Accessed 28 January 2013.
- 10. The metaRegister of Controlled Trials. Available at: www.controlled-trials.com. Accessed 28 January 2013.
- 11. The ClinicalTrials.gov trials registry. Available: www.clinicaltrials.gov. Accessed 28 January 2013.
- 12. The Australian New Zealand Clinical Trials Registry. Available: www.anzctr.org.au. Accessed 28 January 2013.
- 13. The World Health Organization International Clinical Trials Registry platform. Available: www.who.int/trialsearch. Accessed 28 January 2013.
- 14. CentreWatch. Available: http://www.centerwatch.com/. Accessed 28 January 2013.
- 15. Higgins JPT, Altman DG, Sterne JAC, editors (2011) Chapter 8: Assessing risk of bias in included studies. In: Higgins JPT, Green S, editors. Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0 (updated March 2011). The Cochrane Collaboration. Available: www.cochrane-handbook.org. Accessed 28 January 2013.
- 16. Rafii MS, Walsh S, Little JT, Behan K, Reynolds B, et al. (2011) A phase II trial of huperzine A in mild to moderate Alzheimer disease. Neurology 76: 1389–1394.
- 17. Xu SS, Gao ZX, Weng Z, Du ZM, Xu WA, et al. (1995) Efficacy of tablet huperzine-A on memory, cognition and behavior in Alzheimer's disease. Acta Pharmacologica Sinica 16: 391–395.
- 18. Zhou BR, Xu ZQ, Kuang YF, Deng YH, Qian CY (2004) Curative effect of aspirin for postponing the development of Alzheimer's disease. Chinese Journal of Clinical Rehabilitation 8: 3020–3021.
- 19. Zhou BR, Xu ZQ, Kuang YF, Deng YH, Liu ZF (2004) Effectiveness of polydrug therapy for senile dementia. Chinese Journal of Clinical Rehabilitation 8: 1214–1215.
- 20. Liu FG, Fang YS, Gao ZX, Zhou JD, Su ML (1995) Double-blind control treatment of huperzine-A and placebo in 28 patients with Alzheimer disease. Chinese Journal of Pharmacoepidemiology 4: 196–198.
- 21. Zhang ZX, Wang XD, Chen QT, Shu L, Wang JZ, et al. (2002) Clinical efficacy and safety of huperzine A in treatment of mild to moderate Alzheimer disease, a placebo-controlled, double-blind, randomized trial. National Medical Journal of China 82: 941–944.
- 22. Li WN, Yu HY (2011) The efficacy of Huperzine A in treating mild to moderate Alzheimer’s disease. Chinese Journal of Gerontology 31: 2096–2097.
- 23. Yang CY, Lu ZP, Zheng CG (2003) Efficacy and reliability of huperzine A in mild and moderate Alzheimer's disease. Chinese Journal of Clinical Rehabilitation 7: 4258–4259.
- 24. Chai XS, Weng Z, Zhao CY, Zhang SJ (1998) A double-blinded randomized controlled trials on Shuang Yi Ping (Huperzine A) in treating Alzheimer’s disease. Shanghai Medical & Pharmaceutical Journal 1: 16–17.
- 25. Shi BH, Li YF, Li CY, Shi W, Chen XH (2013) Clinical study of huperzine A on patients with mild and moderate Alzheimer disease. Practical Pharmacy And Clinical Remedies 16: 37–38.
- 26. Qin HY, Qu ZF (2008) The relationship between the serum concentration of CHE, SOD and cognitive function in Alzheimer’s disease versus vascular dementia. Shanghai Archives of Psychiatry 20: 339–341.
- 27. Chen YM, Ma YX, Chen MJ, Fang YS, Chai XS, et al. (2000) Observation of aniraletam and huperzine on memory function of Alzheimer’s disease. Modern Rehabilitation 4: 1622–1623.
- 28. Dong HT, Jin YG, Bai Y (2002) Acupuncture for Alzheimer’s disease in 11 cases. ACTC Universitatis Traditionis Medicalis Sinensis Pharmacologiaeque Shanghai 16: 26–28.
- 29. Gu P, Jin QW, Ding XS, Wang Y, Li HJ (2000) Observation of effect on Alzheimer disease treated by Galanthamine hydrobromide capules. Practical Geriatrics 14: 307–308.
- 30. Jia YP, Bai X, Zhang YH, Liu XY (2010) The observation of Alzhermer’s disease by different rules based on blood stasis therapeutic dialectical principle. Chinese Journal of Integrative Medicine on Cardio-/Cerebrovascular Disease 8: 37–39.
- 31. Kuang MZ, Xiao WM, Wang SF, Li RX (2004) Clinical evaluation of huperzine A in improving intelligent disorder in patients with Alzheimer’s disease. Chinese Journal of Clinical Rehabilitation 8: 1216–1217.
- 32. Liu JN, Huang ZY, Zhou YN, Ju YL (1998) The clinical observation of Alzheimer’s disease treated by Huperzine A. . Chinese Journal of Clinical Pharmacy 7: 270–272.
- 33. Huang MZ, Jin F, Zeng JM (2005) Clinic evaluation of huperzine A tablets treating serious Alzheimer’s disease for a period of six months. Chinese Medical Journal of Metallurgical Industry 22: 377–378.
- 34. Yang J, Yang CY, Song C (2012) The effect of Donepezil and Huperzine A in treating Alzheimer’s disease. Chinese Journal of Gerontology 32: 4631–4633.
- 35. Wang WS, Lv JH, Hao ZH, Zhao HF, Tang Z (2009) Clinical study on treatment of dementia by integrative medicine. China Medicine 4: 800–801.
- 36. Schulz KF, Altman DG, Moher D (2010) CONSORT 2010 Statement: updated guidelines for reporting parallel group randomized trials. BMJ 340: c332.
- 37. Chen W, Lim CED, Kang HJ, Liu JP (2011) Chinese herbal medicine for the treatment of Type A H1N1 influenza: a systematic review of randomized controlled trials. PLOS ONE 6: e28093.
- 38. Robert P, Ferris S, Gauthier S, Ihl R, Winblad B (2010) Review of Alzheimer’s disease scales: is there a need for a new multi-domain scale for therapy evaluation in medical practice? Alzheimer’s Research & Therapy 2: 24.
- 39. Tian JZ, Shi J, Zhang XK, Wang YY (2010) Herbal therapy: a new pathway for the treatment of Alzheimer’s disease. Alzheimer’s Research & Therapy 2: 30.