Adverse Effects of Homeopathy

A Systematic Review of Published Case Reports and Case Series

P. Posadzki; A. Alotaibi; E. Ernst


Int J Clin Pract. 2012;66(12):1178-1188. 

In This Article


Our systematic review was aimed at summarising and critically evaluating the available evidence from CS and CR regarding AEs of homeopathy in human patients. According to our findings, homeopathy can lead to AEs, some of which are serious. A recent report on the safety of homeopathy by the European Council for Classical Homeopathy (ECCH) concluded that homeopathy is 'safe to use'. However, this report was incomplete and included only a third of the CRs/CS located by us for the present review.[42] The ECCH-report also commented on the safety of homeopathy relative to conventional treatments. It seems likely that homeopathic remedies cause far less and fewer AEs than conventional drugs, however, such a comparison might be misleading as not the absolute risk of an intervention, but its risk-benefit balance would determine the value of any medical treatment. If the benefit is small or non-existent, even a minute risk would tilt this balance into the negative.

An audit of the Bristol Homeopathic Hospital among 116 patients reported that 11% of them experienced AEs, including headaches, lethargy or vomiting.[43] This percentage figure is difficult to interpret as the authors categorise diarrhoea, eczaema, gastrointestinal upset, hair loss, infections, nausea, migraines, pains, rash, skin irritation, tension headaches, tiredness/fatigue as 'homeopathic aggravations', new symptoms and/or return of old symptoms. Our own review of the evidence for or against the existence of homeopathic aggravations included 24 placebo-controlled trials reporting aggravations, and we came to the conclusion that 'this systematic review does not provide clear evidence that homeopathic aggravations exist'.[44]

In the majority of cases, the possible mechanism of action involved allergic reactions or ingestion of toxic substances. Preparations of heavy metals, such as arsenic, cadmium, mercury or iron, which are frequently used in homeopathy can be toxic,[45] if not highly diluted. Other poisons regularly employed in homeopathy include aconitum, kerosene or thallium, which also can lead to serious health problems in sufficiently low dilutions.

We identified both direct and indirect AEs of homeopathy. The former related to the homeopathic remedy itself and the latter predominantly referred to the replacement of effective conventional therapies with ineffective homeopathic remedies. It was often impossible to distinguish precisely between the two types of AEs. The information whether a fully qualified and registered homeopath applied, the homeopathic remedy was frequently missing. Similarly, other valuable details were often not included in the primary publications. In 94.7% of cases, the potencies were described as below 12 °C, the point beyond which the likelihood of a single molecule being present in the remedy approaches zero. It is plausible that low dilutions of homeopathic preparations cause direct AEs, particularly allergic reactions. One might argue that incidences classified as indirect AEs by us are not truly AEs of homeopathy, but are the result of less than competent healthcare. We have therefore tried to differentiate as clearly as possible between the two. One might also wonder why relatively few indirect AEs have been reported. Most experts view the use of ineffective homeopathic treatments for serious conditions is potentially more harmful than the harm done by homeopathic remedies. One explanation could be that indirect harm of this nature rarely gets reported.Evidence of indirect AEs highlight the need for all homeopaths to be adequately trained such that harm of this nature can be avoided in future.

The preference of homeopathy over conventional medicine when dealing with serious, life-threatening conditions may cause serious harm, and this issue relates to the question of practitioner training.[15,17,26] The treatment of cervical streptococcal lymphadenitis, acute lymphatic leukaemia, bacterial pneumonia and atopic dermatitis with homeopathic remedies is clearly dangerous[4,26,46] simply because homeopathy is not effective for any of these conditions. Other examples of serious conditions that have been treated homeopathically include anxiety,[47] depression,[48] eczema,[49] insomnia,[50] migraine prophylaxis and rheumatic conditions.[51] The fact that such cases are being reported, albeit rarely, seems worrying. Again, we would therefore stress the need for making sure all homeopaths are medically competent.

We were unable to extract the data from one article that combined homeopathy with other modalities, such as herbals and dietary supplements. e.g.;[52] in this retrospective analysis of cases, homeopathy had the second highest hospitalisation index with a total of 255 AEs reported.

Our systematic review has several strengths; we conducted extensive literature searches, did not impose restrictions according to language or time of publication, assessed the reported cases according to predefined criteria and tried to exclude bias where we could. We were able to include more AEs than any previous review has done. However, our systematic review also has a number of important limitations. They pertain to the potential incompleteness of the evidence. AEs of homeopathy are likely to be underreported; therefore, the number of cases summarised herein is less meaningful than the fact that such incidents exist at all. The often low quality of the primary reports further limits the conclusiveness of our findings. Several reports lacked sufficient detail, which renders the interpretation of their findings problematic.[13,15,23,27,28,34,37,38,40] Given such caveats, a cause-effect relationship between the homeopathy and the AEs was frequently difficult to establish. We did not include systematic reviews, clinical trials, surveys and cohort studies in our review.A systematic review of the AEs of homeopathy, concluded that the incidence of AEs of homeopathic remedies was greater than that of placebo in controlled clinical trials; AEs included headache, tiredness, skin eruptions, dizziness, bowel dysfunctions and allergic reactions.[53] Our review of CR and CS is thus not comprehensive. Crucially, it does not tell us anything about the incidence of AEs. Considering the widespread use of homeopathy worldwide and the relative paucity of the reported AEs, it might be very low. Collectively, these limitations render our review less conclusive than we had hoped.

In conclusion, several reports of AEs of homeopathy have been published and some AEs had serious consequences. Clinicians should be aware of the risks associated with homeopathy.