Meta-Analyses and Reviews on Homeopathy

Introduction

A meta-analysis is an overview of primary research that is compiled by statistical means. For this purpose, the research studies are presented in a review according to uniform, statistically ascertainable, comparable criteria and combined in the sum of all individual effect sizes, the effect size. The essential difference to a systematic review is that a review additionally critically analyzes and weights the earlier research data and publications - whereas a meta-analysis only comprises a quantitative and statistical processing of the earlier results. Meta-analyses are performed in all research fields in which empirical data are generated. This includes social sciences, medicine and many natural sciences.

Significance in medicine: Meta-analyses summarize the results of many studies and enable a quantitative statement to be made about the effectiveness and efficacy of a diagnostic or therapy - This applies to all research work on the subject that is included in an overall meta-analysis.

In chronological order, the following meta-analyses and reviews on homeopathy have been published:

• [1] Kleijnen J., Knipschild P., Ter Riet G. (1991, Feb. 9). Clinical trials of homoeopathy. British Medical Journal, 1991;302:316. https://doi.org/10.1136/bmj.302.6772.316
• [2] Linde K., Clausius N., Ramirez G., Melchart D., Eitel F., Hedges L.V., Jonas W.B. (1997, Sep.). Are the clinical effects of homoeopathy placebo effects? A meta-analysis of placebo-controlled trials. The Lancet, Volume 350, ISSUE 9081, P834-843. https://doi.org/10.1016/S0140-6736(97)02293-9
• [3] Cucherat M., Haugh M.C., Gooch M., Boissel J.P. (2000, Apr.). Evidence of clinical efficacy of homeopathy. A meta-analysis of clinical trials. European journal of clinical pharmacology, 56:27–33. https://doi.org/10.1007/s002280050716
• [4] Shang A., Huwiler-Müntener K., Nartey L., Jüni P., Dörig S., Sterne J.A., Pewsner D., Egger M. (2005, Aug. 27). Are the clinical effects of homoeopathy placebo effects? Comparative study of placebo-controlled trials of homoeopathy and allopathy. The Lancet, 366(9487):726- 32. https://doi.org/10.1016/S0140-6736(05)67177-2
• [5] Lüdtke R., Rutten A. L. (2008, Oct. 2) The conclusions on the effectiveness of homeopathy highly depend on the set of analyzed trials. Journal of clinical epidemiology, 61(12):1197-204. https://doi.org/10.1016/j.jclinepi.2008.06.015
• [6] Hahn R. G. (2013, Oct. 17). Homeopathy: Meta-Analyses of Pooled Clinical Data. Forschende Komplementärmedizin, 2013;20:376-81. https://doi.org/10.1159/000355916
• [7] Mathie, R.T., Lloyd, S.M., Legg, L.A. , Clausen J., Moss S., Davidson J.R., Ford I. (2014). Randomised placebo-controlled trials of individualised homeopathic treatment: systematic review and meta-analysis. Syst Rev 3, 142 (2014). https://doi.org/10.1186/2046-4053-3-142

Overview

The following two tables give an overview of the main statements of the most important meta-analyses and reviews. In the following, the most important meta-works are presented and commented.

Table 1: Meta-analyses on homeopathy

Authors	Year	Main statement
Kleijnen et al. [1]	1991	In summary, the evidence for homeopathic therapy is positive, which was a great surprise to the authors. According to current criteria, the available studies are inhomogeneous and partly of lower quality.
Linde et al. [2]	1997	Clear clinical effects of homeopathy. These could not be explained by placebo effects, which is why further research is recommended as useful and necessary.
Cucherat et al. [3]	2000	The effect of homeopathic treatments is above the placebo effect, the statements about the evidence are to be estimated rather low with low methodological quality.
Shang et al. [4]	2005	Despite some good work, he said, the clinical effects of homeopathy are, on balance, pure placebo effects.
Mathie et al. [7]	2014	Individualized homeopathy has a statistically robust and significant specific therapeutic effect, but the effect size is small when the work is rigorously evaluated. Recommendation: Further high-quality research is needed.

This includes the systematic overview (review) by Robert Hahn from 2013 and by Lütke & Rütten 2008.

Table 2: Review on homeopathy

Authors	Year	Main statement
Lüdtke & Rutten [5]	2008	21 studies in the meta-analysis by Shang et al. meet international standards and show a significant positive effect of homeopathy compared to placebo. These studies were discarded in the final analysis by Shang et al. in favour of studies with negative results.
Hahn R. [6]	2013	The equation with placebo effects only succeeds if 90% of the available data remain unconsidered. Furthermore, it is questionable whether meta-analyses, which statistically mix all data with each other, are methodologically exact enough and also produce meaningful results in terms of content.

In the following, the most important meta-analyses are presented and commented.

Comment on the meta-analysis by Linde et al.

In this 1997 meta-analysis [2], the evidence from the 89 studies analyzed is statistically significantly positive in favor of homeopathy (OR: 2.45; 95% CI 2.05 - 2.93). This also includes the subgroup analysis of the 26 studies. This with best quality, turns out clearly positive (OR: 1.66; 95% CI 1.33 - 2.08). The authors comment cautiously and critically and call for further studies, as is usual in science:

“The results of our meta-analysis are not compatible with the hypothesis that the clinical effects of homeopathy are completely due to placebo. However, we found insufficient evidence from these studies that homeopathy is clearly efficacious for any single clinical condition. Further research on homeopathy is warranted provided it is rigorous and systematic.” [2]

Comment on the meta-analysis by Shang et al.

This is a comparative analysis of homeopathy and conventional medicine [4]. The result of the analysis is based on a reduction to 8 studies on homeopathy and 6 studies on conventional medicine.

In the result of the analysis, homeopathy is not superior to the placebo effect, while conventional medicine can show a narrow superiority. If all 110 studies on homeopathy and conventional medicine included at the beginning are used and analyzed, the result is positive for both therapeutic directions.

However, the overall result for all 110 studies is only presented graphically in the funnel plot, the overall statistical result, the odds ratio (OR) is not reported at all.

Unfortunately, this Lancet publication then also lacks information on which 8 or 6 studies were selected for the final analysis, as well as the reasons for the selection. The publication was heavily criticized for this.

It also remains unclear why, of the 26 studies that were described as high quality in the analysis by Linde et al [2], a total of only 8 papers remain here.

Comment on the review of the data by Lüdtke R. and Rutten A. L.

This review by Lüdtke and Rütten [5] shows that 21 studies were of sufficiently good quality according to international standards and that homeopathy was significantly superior to placebo in these 21 studies. At the same time, the studies considered were also very heterogeneous.

The negative result in the above-mentioned analysis by Shang et al. could ultimately be attributed primarily to a study in which marathon runners were treated prophylactically with arnica to prevent muscle soreness. However, this very work is contrary to the principles of homeopathy, as it is a prophylactic measure and not evidence of a curative measure for existing ailments. Such prophylaxis further contradicts the principle of individualization according to the principle of similarity, which is the basis of the homeopathic prescription principle. If the 21 highest quality studies are included, the result is positive in favor of homeopathy, as in the meta-analysis by Linde [2].

Political dimensions

The results of the meta-analysis understandably change with the chosen threshold defining the sample size. Due to the high heterogeneity between the studies used, the results and conclusions of the said meta-analysis are far less clear than presented by the authors.

The meta-analysis by Shang et al [4] caused a great furor, as it was supposed to herald the end of homeopathy. Initially, this seemed to succeed by excluding homeopathy from primary care in Switzerland.

While the first appeals were initially ignored, it was only in the course of the following 3-4 years that the inconsistencies and the lack of scientific seriousness of the analysis gradually came to light.

In skeptical circles of the anti-homeopathy movement, this meta-analysis is still considered standard evidence of the ineffectiveness of homeopathy.

Comment on the review by Robert Hahn

An objective analysis of the available data material and all difficulties of the statistical analysis methods was carried out in 2013 by Robert Hahn [6]. The result of the analysis shows that a missing effect on homeopathy can only be postulated if consistently only 10% of the data are considered, in other words 90% of all papers are excluded. The publication further shows that cross-indication meta-analyses on homeopathy can be fundamentally criticized qualitatively:

Different diseases are treated with different forms of homeopathy and mixed together in the evaluation. Such an approach is not particularly useful in conventional medicine either. No one would think of evaluating, for example, the effectiveness of an appendicitis operation together with a drug treatment to lower blood pressure, in order to then assess the effectiveness of the medicine as a whole.

It would thus make far more sense to use meta-analyses to examine the evidence for homeopathy in relation to individual disease states as well.

Meta-analysis by Mathie et al.

Medicines prescribed in individualized homeopathy are likely to have specific treatment effects that are judged to be statistically small. The results are consistent with subgroup data available in a previous "global" systematic review. The low, or unclear, overall quality of the evidence requires caution in interpreting the results. New high-quality RCT research is needed to provide a more meaningful interpretation. [7]

Comment by Dr. Michael Teut

Here is a commentary on the Mathie et al. meta-analysis by Michael Teut, MD [8]:

"What distinguishes the new meta-analysis from the previous ones?

It is the most up-to-date and comprehensive literature search to date, which also includes databases that were not previously considered or were not available. Exclusively studies on individualized homeopathy (so-called "single remedy homeopathy" or "classical" homeopathy) were included. This was not previously the case.

The heterogeneity of the selected studies was given special consideration in the statistical analysis. The studies were evaluated using a pre-published protocol and were also assessed for the risk of containing a bias.

What results does the new meta-analysis describe?

Randomized and double-blind trials comparing individualized homeopathy versus placebo therapy were evaluated. Complete data sets from 22 of the 32 identified studies were included in the analysis.

A total of 24 diagnoses were treated. On average, 43.5 participants took part in the studies, and a total of 28 outcome parameters were collected in all studies.

For all 22 studies, homeopathy was found to be superior to placebo (odds ratio 1.53 - 95% confidence interval 1.22 - 1.91; p < 0.001). There was no evidence of publication bias in the funnel plot, and statistical heterogeneity was low.

The authors conclude from their analysis that remedies prescribed on the basis of individualized homeopathic remedy finding have a small but specific therapeutic effect.

What is the significance of the new meta-analysis?

It is proven here in a methodologically sound way that the previous studies on individualizing homeopathy show a therapeutic effect that exceeds the so-called placebo effect. The work thus suggests that there is a specific effect of homeopathic medicines. Although this shows only a small additional effect compared to placebos, it is statistically significant." [8]

Comment by the Homeopathy Research Institute (HRI)

So far 6 meta-analyses on homeopathy have been conducted, 5 of them with a positive result that homeopathy is effective beyond the placebo effect. However, further high-quality research is needed to draw more precise and far-reaching conclusions. [9]

By the end of 2023, 286 randomised controlled trials on homeopathy had been published in peer-reviewed journals. Of these, 166 studies are placebo-controlled and investigate the effect on around 100 different diseases. These are eligible for further detailed evaluation with the following result:

42 % of the analysed studies were positive,
3 % were clearly negative and showed no effect of homeopathy and in
55% the result was not clear. [10]

Systematic review of homeopathy by Hamre et al.

A systematic review of these six meta-analyses (MA) has also been available since 2023 (Hamre et al., 2023) .

The subject of the review is the quality assessment of the overall evidence using a catalogue of criteria (GRADE system). For this purpose, the methodology and results of the MAs mentioned are juxtaposed, compared and evaluated in order to achieve a more differentiated understanding and greater certainty than is possible through the isolated effectiveness assessment of an individual MA.

The following is a summary of the article by Kiene, Hamre & Martin 2024 on the aforementioned review.

The analysis shows that five of the six meta-analyses provide a summarised effect estimate for all included studies. All five showed significant positive effects for homeopathy.

Four MAs carried out an effect estimate after restricting themselves to studies with higher methodological quality. In three analyses, the significant positive effects of homeopathy remained, in one MA the effect remained positive but not significant. The methodological quality of the homeopathy studies was similar or higher than that of other clinical studies from a comparable time period with the same design and identical evaluation criteria.

The categorisation of the overall evidence for homeopathy (high / moderate / low / very low) was

• high for individualized homeopathy (examined in two MAs),
• moderate for non-individualized homeopathy (one MA) and
• moderate for any homeopathy (three MA with MIX).

After restricting the sources of evidence to the three MAs with the lowest risk of bias, the quality of the overall evidence for all homeopathy was categorised as high, while the other classifications remained unchanged. The overview shows 53% positive and potentially positive versus 44% ineffective results.

Discussion of the review

The review was commented on in the open review of the publication manuscript (journal Systematic Reviews) with:

"The author's research is rigorous and has strong data analysis skills" and "This is an extremely detailed and well written systematic review of meta-analyses of trials in homeopathy". (Hamre et al. (2023). Peer Review Reports; Author comments - Harald Johan Hamre; Report 17 Jun 2023).

Disparagingly critical comments on this review are based on ignorance or misunderstanding of the methodology of a systematic review of MA. Authors' comment:

The same applies to statements made by the applicant against homeopathy at the Doctors' Conference. It was claimed that the review would carry out a new effect estimate of all studies of the six MAs and make multiple use of studies, which is why "only an apparent positive result was obtained by multiplying a few positive studies". It is true that the review did not contain any new effect estimates of individual studies, but only assessments of the six MAs according to the GRADE system. [13]

Analysis of the clinical effectiveness of homeopathy by Bonamin et al.

In the work by Bonamin et al. from 2024, analyses of all systematic reviews on homeopathy from 1991 - 2021 are presented graphically in an online evidence gap map.

Of 231 identified systematic reviews (SR), 51 were fully analysed. All studies that were categorised by the respective authors as having a high risk of BIAS were not included in the analysis.

Methodology and results

The methodological quality was assessed using the AMSTAR-2 criteria^[1] for the confidence level of the SR: positive, potentially positive, ineffective, inconclusive or negative.

The diversity of scattered results and the limited number of studies with a considerable heterogeneity of interventions, results and protocols are a fundamental structural feature of the homeopathic literature and represented the main problem of the evaluation, which is why ultimately 42 of the selected 51 studies (82.4 %) could not be used for comparison.

For this reason, specific details reported in the systematic reviews were also included in order to increase the sensitivity of the analysis. Finally, the highest quality systematic reviews and the studies cited in them were listed and should serve as helpful examples for future clinical work.

In future, the definition of standard operating procedures as a guide to good clinical practice will be necessary to promote the international reproducibility and comparability of results.

The results of this review nevertheless point to interesting aspects that fundamentally question established opinions in the discussion about homeopathy research:

1. Almost all SRs have been published in high-ranking journals, as can be seen from the Scientific Journal Ranking[2] (SJR) with an impact factor[3] (IF) of 9.38. The scientific literature on homeopathy is therefore on a par with other biomedical sciences, albeit less extensive overall.
2. In total, there exists a remarkable number of studies on the individualized therapeutic approach. Approximately 27% of the intervention outcomes and about half of the highest-quality primary studies in the systematic reviews focused on individualized homeopathy (iHom). Thus, iHom emerges as the gold standard for treatment and should be further researched as a focal point.
3. A broad spectrum of illnesses is recorded in the SR, without one area dominating: chronic illnesses 17%; infections 15%; metabolic disorders 13%; pain 11%; mental complaints 8%; diseases of the reproductive organs 7%; dental health 7%; quality of life and well-being 7%; other 15%.
4. In most studies, the aspect of well-being and quality of life was only minimally researched, which is surprising in relation to the holistic approach of iHom. Future studies should investigate this in more detail with good standards.

Difficulties in analysing iHom studies

In summary, two aspects stand out:

1. The prescription methodology is often not described precisely enough as to what exactly was individualized and how.
2. The ability of prescribers to prescribe appropriately is not tested
3. Clinical parameters associated with adaptation responses are rarely considered in most homeopathy research protocols.

This discrepancy primarily has two reasons. On the one hand, homeopathic professionals lack knowledge of clinical and epidemiological research, leading to inconsistencies in the design of studies. On the other hand, professionals in conventional clinical and epidemiological research are unfamiliar with the phenomenological methodology of individualized homeopathy (iHom).

For these reasons, essential characteristics - such as how living systems respond as a whole to iHom stimuli, which is often associated with greater robustness to harmful stimuli - are not adequately captured. Particularly, clinical improvements that occur over time as a result of adaptive responses are not taken into account in the study evaluations.

Summary

The heterogeneity of previous studies can be well explained by this complexity. Many studies, therefore, result in unsatisfactory outcomes because the research approaches used and the alignment of parameters are not well suited to the topic, and the research materials were compiled inconsistently.

The work of Bonamin et al. (2024) arrives at similar conclusions using the applied assessment scale (AMSTAR-2) as the parallel systematic review by Hamre et al. (2023), which used a different assessment scale (GRADE). The distribution of the results - positive, potentially positive and ineffective - does not differ significantly, which confirms the impartiality of the assessments.

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[1] Lorenz, R., Matthias, K., Pieper, D., Wegewitz, U., Morche, J., Nocon, M., Rissling, O., Schirm, J., & Jacobs, A. (2019). The AMSTAR 2 quality assessment tool: How meaningful is the overall assessment of the confidence in the review results and which items are particularly important? EbM and Digital Transformation in Medicine; 20th Annual Conference of the German Network for Evidence-based Medicine. https://doi.org/10.3205/19EBM109

[2] The Scientific Journal Ranking (SJR) evaluates journals according to their scientific influence on the basis of a citation analysis and the prestige of a journal.

[3] Impact factor IF - calculated figure for the citation frequency of a scientific journal, values above 10 are considered outstanding.

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Sources and References

[1] Kleijnen J., Knipschild P., Ter Riet G. (1991, Feb. 9). Clinical trials of homoeopathy. British Medical Journal, 1991;302:316. https://doi.org/10.1136/bmj.302.6772.316

[2] Linde K., Clausius N., Ramirez G., Melchart D., Eitel F., Hedges L.V., Jonas W.B. (1997, Sep). Are the clinical effects of homoeopathy placebo effects? A meta-analysis of placebo-controlled trials. The Lancet, Volume 350, ISSUE 9081, P834-843. https://doi.org/10.1016/S0140-6736(97)02293-9

[3] Cucherat M., Haugh M.C., Gooch M., Boissel J.P. (2000, Apr.). Evidence of clinical efficacy of homeopathy. A meta-analysis of clinical trials. European journal of clinical pharmacology, 56:27–33. https://doi.org/10.1007/s002280050716

[4] Shang A., Huwiler-Müntener K., Nartey L., Jüni P., Dörig S., Sterne J.A., Pewsner D., Egger M. (2005, Aug. 27). Are the clinical effects of homoeopathy placebo effects? Comparative study of placebo-controlled trials of homoeopathy and allopathy. The Lancet, 366(9487):726- 32. https://doi.org/10.1016/S0140-6736(05)67177-2

[5] Lüdtke R., Rutten A. L. (2008, Oct. 2) The conclusions on the effectiveness of homeopathy highly depend on the set of analyzed trials. Journal of clinical epidemiology, 61(12):1197-204. https://doi.org/10.1016/j.jclinepi.2008.06.015

[6] Hahn R. G. (2013, Oct. 17). Homeopathy: Meta-Analyses of Pooled Clinical Data. Forschende Komplementärmedizin, 2013;20:376-81. https://doi.org/10.1159/000355916

[7] Mathie, R.T., Lloyd, S.M., Legg, L.A. , Clausen J., Moss S., Davidson J.R., Ford I. (2014). Randomised placebo-controlled trials of individualised homeopathic treatment: systematic review and meta-analysis. Syst Rev 3, 142 (2014). https://doi.org/10.1186/2046-4053-3-142

[8] Teut M. (2014, Dec. 8). Neue Metaanalyse: Individualisierte Homöopathie signifikant besser als Placebo. Retrieved June 13, 2022, from https://www.informationen-zur-homoeopathie.de/?p=862

[9] Clinical trials overview? Homeopathy Research Institut. Retrieved on 1. November 2019, von www.hri-research.org/de (Current contribution, available https://www.hri-research.org/resources/essentialevidence/clinical-trials-overview/ checked on 7 May 2025)

[10] What scientific evidence is there that homeopathy works? Homeopathy Research Institut. Retrieved on May 7, 2025, from https://www.hri-research.org/resources/homeopathy-faqs/scientific-evidence-for-homeopathy/

[11] Hamre, H. J., Glockmann, A., von Ammon, K., Riley, D. S., & Kiene, H. (2023). Efficacy of homoeopathic treatment: Systematic review of meta-analyses of randomised placebo-controlled homoeopathy trials for any indication. Systematic Reviews, 12(1), 1–24. https://doi.org/10.1186/s13643-023-02313-2

[12] Hamre et al. (2023). Peer Review Reports From: Efficacy of homoeopathic treatment: Systematic review of meta-analyses of randomised placebo-controlled homoeopathy trials for any indication. Accessed on May 29, 2025, from https://systematicreviewsjournal.biomedcentral.com/articles/10.1186/s13643-023-02313-2/peer-review

[13] Kiene, H., Hamre, H. J., & Martin, D. (2024, Juni). Auch die Homöopathie hat einen berechtigten Platz in der wissenschaftsbasierten Medizin! In AerzteZeitung.de. Accessed on March 13, 2025, from https://www.aerztezeitung.de/Politik/Auch-die-Homoeopathie-hat-einen-berechtigten-Platz-in-der-wissenschaftsbasierten-Medizin-450358.html

[14] Bonamin, L. V., Adler, U. C., Vilhena, E. C. D., Quaresma, C. H., Oliveira, A. P. D., Coimbra, E. N., Hosomi, J. K., Abdala, C. V. M., Schveitzer, M. C., Portella, C. F. S., & Ghelman, R. (2024). Presentation and Analysis of the Online Evidence Gap Map, “Clinical Effectiveness of Homeopathy”. Homeopathy, s-0044-1791490. https://doi.org/10.1055/s-0044-1791490

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Authors: glt | Rev.: TBD | Ed.: pz | last modified May 29, 2025