Tests of the efficacy of homeopathy
Tests of the efficacy of homeopathy have taken many different forms, with inconsistent outcomes. By comparison with contemporary trials of conventional medicines, tests of homeopathic remedies are very small (i.e. on relatively few subjects), and often are poorly controlled (without double-blinding, placebo controls, or objective outcomes). These weaknesses mean that positive results are generally treated with skepticism by scientists and conventional physicians. Positive results are usually reported in the homeopathic literature, and seldom in conventional academic medical journals; the trials referenced here however were all published in the conventional literature.
In the U.S.A., the National Center for Complementary and Alternative Medicine (NCCAM), part of the National Institutes of Health, funds some research into homeopathy. It states that controlled clinical trials of homeopathy have produced mixed results; in some, homeopathy appeared to be no more helpful than a placebo, but in others, more benefits were seen than expected from a placebo.
  NCCAM's acting deputy director, Jack Killen, said, in a Newsweek article, homeopathy "goes beyond current understanding of chemistry and physics." He added, "There is, to my knowledge, no condition for which homeopathy has been proven to be an effective treatment." .
Cochrane Reviews did a meta-analysis of seven randomized controlled trials, three prevention trials (number of participants, ) and four treatment trials, . The authors considered only two were statistically adequate, but data from the prevention trials showed no effect. Data from the treatment trials showed enough evidence of efficacy that further trials were recommended, but that the remedy could not be recommended for first-line therapy. 
In the UK, the NHS recognizes that there have been about 200 randomised controlled trials evaluating homeopathy, some show efficacy of treatment and some don't. They conclude, "Despite the available research, it has proven difficult to produce clear clinical evidence that homeopathy works".
Randomized controlled trials in humans
Clinical trials are the "gold standard" for efficacy in mainstream medicine, often creating an impasse with homeopaths who do not find their paradigm compatible with large scale randomized controlled trials. Homeopaths assert that homeopathic remedies generally have to be individually prescribed to a sick person based on the totality of symptoms, not just the disease that he/she has been diagnosed with; they therefore argue that many clinical trials are inappropriate tests for homeopathic treatment, but acknowledge that there are sometimes exceptions to the need for individualization (the experience above with Oscillococcinum is one such exception).
Some individual RCTs have shown no statistically significant effect, while others indicate a positive difference in people receiving homeopathic treatment. There are single RCTs in favor of homeopathy for a number of other conditions, including: respiratory allergies such as hayfever, asthma and perennial allergic rhinitis,  acute otitis media, influenza, childhood diarrhea, symptoms of chronic obstructive pulmonary disease, arthritis, fibromyalgia,  vertigo, head injuries, varicose veins  ankle sprain, bronchitis, chronic fatigue and premenstrual syndrome.
Some trials have been performed that partially meet these criteria, and some of these have reported positive effects. These have not been considered as providing compelling evidence, partly because of deficiencies in trial design, but mainly because of the possibility of publication bias - the phenomenon whereby trials that happen by chance to appear to show a positive outcome are more likely to be published than those which are inconclusive or appear to show a negative outcome.
Meta-analyses on humans
Some authors of meta-analyses have concluded that the placebo response is an inadequate explanation for the positive responses that have been reported in some trials. For example, one review  assessed 105 trials, 81 of them positive; the authors concluded that the evidence on balance is that trials are positive but not sufficient to draw definite conclusions, and they said that “based on this evidence we would be ready to accept that homeopathy can be efficacious, if only the mechanism of action were more plausible”.
In another review, Linde and colleagues analyzed 89 trials and found a mean odds ratio of 2.45 (95% confidence interval, 2.05–2.93) in favor of homeopathy. When considering just those trials of “high quality” and after correcting for publication bias, the findings remained significant (means odds ratio of 1.86), however, the main conclusion was that the results “were not compatible with the hypothesis that the effects of homeopathy are completely due to placebo.” The authors also concluded that the higher quality trials were less likely to be positive than those of lower quality, saying “There is increasing evidence that more rigorous trials tend to yield less optimistic results than trials with less precautions against bias.”
The Lancet controversy
In 2005, the Lancet published a meta-analysis of 110 placebo-controlled homoeopathy trials and 110 matched conventional-medicine trials.  . The authors concluded that homeopathy was no better than placebo, and suggested that no further research on homeopathy is necessary. The article was accompanied by an unsigned editorial titled “The end of homeopathy" and another, signed, editorial.
While Shang was the lead author, the work was done under the Swiss Complementary Medicine Evaluation Programme (Programm Evaluation Komplementärmedizin, PEK). The outcome suggested that the clinical effects of homeopathic remedies might all be placebo effects. The Lancet study is notable as a "global" meta-analysis of homeopathy, not an analysis of particular remedies, i.e. it tested the hypothesis that all of the reported effects of homeopathic remedies are placebo effects. If so, then reports of positive effects reflect publication bias (the tendency to publish results when they show a positive effect but not when they are negative), and the magnitude of such effects should diminish with sample size and study quality. They analyzed an equal number of conventional medicine trials similarly; these showed a real effect of treatment, in that the size of the reported effect was independent of sample size, but the trials of homeopathy remedies did not. The study does not prove that homeopathy is never effective, but is consistent with the interpretation that all reported effects are placebo effects. The Lancet subsequently published a selection of critical correspondence.
Several meta-analyses evaluating the homeopathic treatment of specific diseases have also found positive results. These studied childhood diarrhea,  respiratory allergies , and postoperative ileus. 
In one meta-analysis of 6 trials , there were six RCTs, which used different treatments that were difficult to form into a meaningful pool. The authors observed that they used standardized treatment, which probably differs from the homeopathic standard of practice. They observed "There has been only a limited attempt to measure a 'package of care' effect (i.e., the effect of the medication as well as the consultation, which is considered a vital part of individualised homeopathic practice)." The conclusion was that there was not enough useful data, and strongly recommended, in addition to RCTs, collecting "observational data to document the different methods of homeopathic prescribing and how patients respond. This will help to establish to what extent people respond to a 'package of care' rather than the homeopathic intervention alone."  In conventional medicine, there have been comparisons where the actual treatment was the same, but the variable was the type of encounter (e.g., short or long, physician specialist vs. generalist, nurse-educator rather than physician).
Another study identified 17 useful articles. Six, however, re-analyzed the same major meta-analysis. This major study observed some differences between homeopathic treatment and placebo, but could find no specific evidence of efficacy for any specific condition. The authors of this meta-analysis defined "evidence" in this context as having at least three independent researchers finding positive results from a specific treatment. The meta-analysis of the 17 papers concluded "Until more compelling results are available, homeopathy cannot be viewed as an evidence-based form of therapy." 
Are the right things being analyzed?
An observation from some authors was that a key element missed in many studies was a systematic observation of the the interaction between homeopath and patient, in contrast with the interaction between patient and conventional health care worker. In conventional medicine, there is concern within the U.S. healthcare economics area about even collecting minimal data on the quality of encounters. One policy study stressed the need not to understand the nature of the interaction, but even to get basic demographics on the encounter;especially in programs servicing low-income populations, there may be little more than billing data. There are a number of trial programs to use nurses and other providers, at a lower cost than physicians, to do case management of chronic disease. Case management interactions may be as long as some of those with homeopaths. It is not unreasonable to note that a number of nursing associations call for more holistic patient interactions than is typical for conventional medicine, and to wonder if there most important lessons from current homeopathy, which are not being studied.
- National Center for Complementary and Alternative Medicine, What has scientific research found out about whether homeopathy works?, Questions and Answers About Homeopathy
- The funded studies include:
- A study on fibromyalgia, which showed clinical benefits from individually chosen homeopathic remedies as well as objective differences in EEG readings in homeopathic and placebo subjects. (Bell IR et al. (2004) Improved clinical status in fibromyalgia patients treated with individualized homeopathic remedies versus placebo, Rheumatology :1111-7
- Bell IR et al. (2004) EEG Alpha sensitization in individualized homeopathic treatment of fibromyalgia. Int J Neurosci 114:1195-220)
- A study on homeopathy for mild traumatic brain injury. (Chapman E et al. (1999) Homeopathic treatment of mild traumatic brain injury: a randomized, double-blind, placebo-controlled trial J Head Trauma Rehab14:521-42) This pilot study indicate a significant benefit from the homeopathic treatment but requires large-scale, independent replication.)
- Adler, Jerry (February 4, 2008), "No Way to Treat the Dying", Newsweek
- Vickers AJ, Smith C. (2006), "Homoeopathic Oscillococcinum for preventing and treating influenza and influenza-like syndromes.", Cochrane Database Syst Rev., DOI:10.1002/14651858.CD001957.pub3 DOI: 10.1002/14651858.CD001957.pub3
- NHS Direct, Homeopathy, Health Encyclopedia
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- Weiser M et al. (1998) Homeopathic vs. conventional treatment of vertigo: a randomized double-blind controlled clinical study Archives Otolaryngol 124:879-85
- Chapman E et al.(1999) Homeopathic treatment of mild Traumatic brain injury: a randomized, double-blind, placebo-controlled trial J Head Trauma Rehab 6:521-42
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- Linde K et al., "Are the clinical effects of homoeopathy placebo effects? A meta-analysis of placebo-controlled trials", Lancet 350: 834–43
- Shang A et al. (2005). "Are the clinical effects of homoeopathy placebo effects? Comparative study of placebo-controlled trials of homoeopathy and allopathy". Lancet 366: 726-32. PMID 16125589.
- Boseley, Sarah (August 26 2005), "As a fourth study says it's no better than a placebo, is this the end for homeopathy?", The Guardian
- Editorial (2005) The end of homeopathy Lancet 366:690
- Vandenbroucke JP (2005) Homoeopathy and ‘the growth of truth’ Lancet 366:691–2
- Jacobs J et al. (2003) Homeopathy for childhood diarrhea: combined results and metaanalysis from three randomized, controlled clinical trials. Pediatric Infectious Disease Journal 22:229–34.
- Taylor MA et al. (2000)Randomised Controlled trial of homoeopathy versus placebo in perennial allergic rhinitis with overview of four trial series BMJ 321:471-76
- Barnes J et al. (1997) Homeopathy for postoperative ileus? A meta-analysis. J Clin Gastroenterol 25:628–33
- McCarney RW et al. (2004). "Homeopathy for chronic asthma". Cochrane database of systematic reviews: CD000353. DOI:10.1002/14651858.CD000353.pub2. PMID 14973954. Research Blogging.
- Ernst E (2002). "A systematic review of systematic reviews of homeopathy". Br J Clin Pharmacol 54: 577–82. PMID 12492603.
- McGlynn, EA (April 2008), "[http://www.ahrq.gov/qual/efficiency/efficiency.pdf Final Report: Identifying, Categorizing, and Evaluating Health Care Efficiency Measures]", Southern California Evidence-based Practice Center—RAND Corporation, Santa Monica, CA, AHRQ Publication No. 08-0030
- Care Management Institute Committee, American Association of Managed Care Nurses (AAMCN) (2007), Care Management Guidelines