Homeopathy: what does the “best” evidence tell us?
Edzard Ernst
he debate about the value of homeo- ABSTRACT pathy — a therapeutic method that Objective: To evaluate the evidence for and against the effectiveness of homeopathy. often uses highly diluted prepara- T Data sources: The Cochrane Database of Systematic Reviews (generally considered tions of substances whose effects when administered to healthy subjects correspond to be the most reliable source of evidence) was searched in January 2010. to the manifestation of the disorder in the Study selection: Cochrane reviews with the term “homeopathy” in the title, abstract unwell patient1 — is as old as homeopathy or keywords were considered. Protocols of reviews were excluded. Six articles met the itself. In recent decades, about 150 control- inclusion criteria. led clinical trials of homeopathy have been Data extraction: Each of the six reviews was examined for specific subject matter; published. The results were neither all nega- number of clinical trials reviewed; total number of patients involved; and authors’ tive nor all positive. In such situations, some conclusions. The reviews covered the following conditions: cancer, attention-deficit commentators resort to “cherry picking” — hyperactivity disorder, asthma, dementia, influenza and induction of labour. choosing those findings that fit their own Data synthesis: The findings of the reviews were discussed narratively (the reviews’ preconceptions. The problem of selective clinical and statistical heterogeneity precluded meta-analysis). citation is most effectively overcome by eval- Conclusions: The findings of currently available Cochrane reviews of studies of uating all reliable evidence, an aim best met homeopathy do not show that homeopathic medicines have effects beyond placebo. by systematic reviews. Even at the level of systematic reviews, MJA 2010; 192: 458–460 the evidence on homeopathy is not entirely uniform. For instance, a Lancet review of 1997 concluded that “the clinical effects of articles in full and extracted key data the effectiveness of homeopathic remedies. homeopathy are not completely due to pla- according to predefined criteria: subject These reviews, being Cochrane reviews, are cebo”,2 while another systematic review, matter; number of clinical trials reviewed; likely to be more reliable than other sources 6 published in the same journal in 2005, total number of patients involved; and of evidence. Furthermore, as most were concluded that “the clinical effects of home- authors’ conclusions. I considered under- authored by homeopaths, it seems unlikely opathy are placebo effects”.3 In 2002, I taking a meta-analysis but, because of the that they were biased against homeopathy. conducted a systematic review of 17 system- clinical and statistical heterogeneity of the In fact, one might argue that they were atic reviews and concluded that “the best primary data, abandoned this plan. biased in favour of homeopathy. For clinical evidence for homeopathy available instance, the conclusion that “it is not possi- 14 to date does not warrant positive recom- ble to comment . . .” on the basis of an RESULTS mendations of its use in clinical practice”.4 “empty” review (a review that did not Homeopaths have argued that systematic The search generated 13 hits. I excluded include a single primary study) might have reviews that fail to generate positive conclu- four articles because they were not specifi- been phrased more critically. The authors 7-10 sions about homeopathy are biased.5 It is cally about homeopathy, and three could have pointed out that, whenever no therefore necessary to seek out those sys- because they were protocols of systematic trial data exist, it makes little sense to use tematic reviews of research into homeopathy reviews in progress. Six systematic reviews homeopathy (or any other therapy) for 11-16 that are least likely to be biased. Several were included (Box). dementia (or any other condition). authors have demonstrated that Cochrane The six articles that met the inclusion Many systematic reviews of homeopathy reviewsThe tend Medical to be Journalsuperior of to Australia other reviews; ISSN: 0025-criteria related to the following conditions: have been published outside the Cochrane 11 they are729X more 19 April rigorous, 2010 192more 8 458-460transparent, cancer, attention-deficit hyperactivity dis- database. Most arrive at similarly negative 12 13 14 15 3,4,17 less biased©The andMedical more upJournal to date. of6 InAustralia a word, 2010order, asthma, dementia, influenza conclusions and, in recent years, the 16 they mightwww.mja.com.au be considered the “best”. There- and induction of labour. Most were evidence seems to have become less and less Systematic Review 18 fore, the aim of this article is to summarise authored or coauthored by homeopaths. convincing. Numerous authors have and appraise the findings from Cochrane Key data from these reviews are summarised pointed out that the main assumptions of 19 reviews of studies of homeopathy. in the Box. None of these articles concluded homeopathy are biologically implausible. that homeopathy is an effective treatment. Reviewers of basic research studies of home- One review15 was recently withdrawn from opathy have noted the low quality of the METHODS the database as the authors were unable to data and lack of replications,20 and others I searched the Cochrane Database of Sys- update it. For the purpose of this overview, I have concluded that “no positive result was tematic Reviews in January 2010 for reviews have therefore used the 2006 version of that stable enough to be reproduced by all inves- that had the term “homeopathy” in their article.15 tigators”.21 These findings indicate that title, abstract or keywords. Articles were homeopathic remedies are unlikely to have excluded if they referred to protocols only, clinical effects beyond placebo. Homeopaths or if they were not specifically about home- DISCUSSION tend to deny this and produce lower-level opathy but included it among other forms of Collectively, the six reviews that I appraised evidence to the contrary.22,23 Closer inspec- health care for a given condition. I read all failed to provide compelling evidence for tion of this evidence, however, regularly
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Cochrane systematic reviews of studies of homeopathy
No. of included First author Stated trials (total no. Authors’ (year published) Subject objective of patients) conclusions Appraisal Kassab Adverse effects of “Evaluate effectiveness and safety 8 (664) “This review found The two remedies (2009)11 cancer treatments of homeopathic medicines used preliminary data in supported by good to prevent or treat adverse effects support . . .” evidence were not of cancer.” highly diluted Heirs Attention-deficit “To assess the safety and effectiveness 4 (168) “There is currently little No significant (2007)12 hyperactivity of homeopathy as a treatment for evidence for the efficacy benefit disorder attention-deficit hyperactivity disorder.” of homeopathy . . .” McCarney Chronic asthma “ . . . to assess the effects of 6 (556) “There is not enough No significant (2004)13 homeopathy in people with chronic evidence …” benefit stable asthma.” McCarney Dementia “To evaluate the effectiveness and 0 (0) “. . . it is not possible to An “empty” review (2003)14 safety profile of homeopathically comment on the use of (no primary data) prepared medications used in homeopathy in treating treating dementia . . .” dementia.” Vickers Oscillococcinum “Determine whether homoeopathic 7 (2265) “Though promising the Only review (2006)15 for preventing and Oscillococcinum or similar medicines data were not strong to include a treating influenza are more effective than placebo in the enough . . .” meta-analysis; and influenza-like prevention and treatment of influenza no significant benefit syndromes and influenza-like syndromes” Smith Induction of “To determine the effects of 2 (133) “There is insufficient Both primary studies (2003)16 labour homoeopathy for third trimester cervical evidence to recommend were flawed; no ripening or induction of labour.” the use of homeopathy as significant benefit a method of induction”
reveals bias. For instance, one reviewer devoid of pharmacologically active ingredi- tive medicine. 2nd ed. Edinburgh: Elsevier deliberately set out to select only the posi- ents, some homeopathic remedies do con- Mosby, 2006. tive evidence and omit all negative evi- tain active molecules. One could thus 2 Linde K, Clausius N, Ramirez G, et al. Are the 22 clinical effects of homoeopathy placebo dence. manufacture a homeopathic preparation of effects? A meta-analysis of placebo-controlled Homeopaths also point to observational aspirin that is pharmacologically identical to trials. Lancet 1997; 350: 834-843. studies that seem to suggest that homeopa- conventional aspirin. It is not surprising that 3 Shang A, Huwiler-Muntener K, Nartey L, et al. thy is effective.23 Some then tend to inter- such medicines can have pharmacological Are the clinical effects of homoeopathy pla- effects, but concluding that homeopathic cebo effects? Comparative study of placebo- pret the discrepancy between this evidence controlled trials of homoeopathy and allopathy. and that from controlled studies in a most medicines are effective, on the basis of such Lancet 2005; 366: 726-732. unusual way: they claim it shows that the data, would be misleading. 4 Ernst E. A systematic review of systematic controlled clinical trial is not suited for the In conclusion, the most reliable evidence reviews of homeopathy. Br J Clin Pharmacol study of homeopathy and that observational — that produced by Cochrane reviews — 2002; 54: 577-582. data demonstrate the true value of homeop- fails to demonstrate that homeopathic medi- 5 Rutten AL, Stolper CF. The 2005 meta-analysis 23 of homeopathy: the importance of post-publi- athy. A more rational explanation would cines have effects beyond placebo. cation data. Homeopathy 2008; 97: 169-177. be that the positive outcomes of observa- 6 Olsen O, Middleton P, Ezzo J, et al. Quality of Cochrane reviews: assessment of sample from tional studies are caused by the non-specific COMPETING INTERESTS effects of homeopathic treatments (eg, the 1998. BMJ 2001; 323: 829-832. None identified. 7 Smith CA, Collins CT, Cyna AM, Crowther CA. empathic and lengthy consultation typical of Complementary and alternative therapies for homeopathic services), while the controlled pain management in labour. Cochrane Data- trials demonstrate that homeopathic reme- AUTHOR DETAILS base Syst Rev 2006; (4): CD003521. doi: dies are placebos.21,24,25 Edzard Ernst, FMedSci, FRCP, FRCPEd, 10.1002/14651858.pub2. The Cochrane review by Kassab and Director 8 Glazener CM, Evans JH, Cheuk DK. Comple- 11 Complementary Medicine, Peninsula Medical mentary and miscellaneous interventions for colleagues found preliminary evidence in nocturnal enuresis in children. Cochrane Data- School, University of Exeter, Exeter, United support of homeopathy (Box). This evi- base Syst Rev 2005; (2): CD005230. doi: Kingdom. dence resulted from studies of material dilu- 10.1002/14651858. Correspondence: [email protected] tions. However, if dilutions are prepared 9 Gagnier JJ, van Tulder M, Berman B, Bombar- according to homeopathic rules, they are dier C. Herbal medicine for low back pain. Cochrane Database Syst Rev 2006; (2): technically homeopathic remedies even if REFERENCES CD004504. doi: 10.1002/14651858.pub3. they are not highly diluted. This means that, 1 Ernst E, Pittler MH, Wider B, Boddy K. The 10 van der Wouden JC, Menke J, Gajadin S, et al. while a typical homeopathic remedy is desktop guide to complementary and alterna- Interventions for cutaneous molluscum conta-
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giosum. Cochrane Database Syst Rev 2006; (2): Syst Rev 2006; (3): CD001957. doi: 10.1002/ ture. Complement Ther Med 2007; 15 (2): 128- CD004767. doi: 10.1002/14651858.pub2. 14651858. 138. 11 Kassab S, Cummings M, Berkovitz S, et al. 16 Smith CA. Homoeopathy for induction of 22 European Network of Homeopathy Research- Homeopathic medicines for adverse effects of labour. Cochrane Database Syst Rev 2003; (4): ers. An overview of positive homeopathy cancer treatments. Cochrane Database Syst CD003399. doi: 10.1002/14651858. research and surveys. March, 2007. http:// Rev 2009; (2): CD004845. doi: 10.1002/ 17 Altunc U, Pittler MH, Ernst E. Homeopathy for www.homeopathy-soh.org/whats-new/ 14651858.pub2. childhood and adolescence ailments: system- research/documents/PositiveHomRe- 12 Heirs M, Dean ME. Homeopathy for attention atic review of randomized clinical trials. Mayo search.PDF. deficit/hyperactivity disorder or hyperkinetic Clin Proc 2007; 82 (1): 69-75. 23 Spence DS, Thompson EA, Barron SJ. Homeo- disorder. Cochrane Database Syst Rev 2007; (4): 18 Ernst E, Pittler MH, Wider B, Boddy K. Home- pathic treatment for chronic disease: a 6-year, CD005648. doi: 10.1002/14651858.pub2. opathy: is the evidence-base changing? Per- university-hospital outpatient observational 13 McCarney RW, Linde K, Lasserson TJ. Homeop- fusion 2006; 19: 380-382. study. J Altern Complement Med 2005; 11: 793- athy for chronic asthma. Cochrane Database 19 Ernst E, editor. Healing, hype or harm? A critical 798. Syst Rev 2004; (1): CD000353. doi: 10.1002/ analysis of complementary or alternative medi- 24 Ernst E. The truth about homeopathy. Br J Clin 14651858.pub2. cine. Exeter: Imprint Academic, 2008. Pharmacol 2008; 65: 163-164. 14 McCarney R, Warner J, Fisher P, Van Haselen R. 20 Linde K, Jonas WB, Melchart D, et al. Critical Homeopathy for dementia. Cochrane Data- review and meta-analysis of serial agitated dilu- 25 Overall KL, Dunham AE. Homeopathy and the base Syst Rev 2003; (1): CD003803. doi: tions in experimental toxicology. Hum Exp Tox- curse of the scientific method. Vet J 2009; 180: 10.1002/14651858. icol 1994; 13: 481-492. 141-148. 15 Vickers AJ, Smith C. Homoeopathic Oscillococ- 21 Witt CM, Bluth M, Albrecht H, et al. The in vitro cinum for preventing and treating influenza and evidence for an effect of high homeopathic influenza-like syndromes. Cochrane Database potencies — a systematic review of the litera- (Received 30 Sep 2009, accepted 19 Jan 2010) ❏
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