Nux vomica, a homeopathic remedy, contains strychnine, which is derived from the seeds of the Asian Strychnos nux-vomica tree and often used as rat poison. Ingestion of strychnine can lead to nausea and muscle twitching that progress rapidly to vomiting, loss of consciousness, and fatal convulsions. But the homeopathic nux vomica dilution, in which only a few, if any, strychnine molecules remain, is used to relieve symptoms similar to those that ingestion of undiluted strychnine causes: irritability, muscular tension, and digestive upset. This exemplifies the "law of similars," on which homeopathic medicine is based: like cures like.
The Homoeopathic Pharmacopoeia Convention of the United States (HPCUS), a nonprofit organization, defines homeopathy as "the art and the science of healing the sick by using substances capable of causing the same symptoms, syndromes, and conditions when administered to healthy people. The underlying philosophy of homeopathy, sometimes called vitalism, holds that the body possesses the power to heal itself (sometimes called the vital force) and that disruptions to that vital force may result in some degree of pathology (acute or chronic). Homeopathy uses microdoses of substances to stimulate that force and promote healing.
The law of similars (similia similibus curentur or "like cures like"), a cornerstone of homeopathic philosophy, can be traced to Hippocrates in 400 bc and Paracelsus in the 16th century , among others. About 200 years ago Samuel Hahnemann, a German physician, rediscovered this principle, observing that when he repeatedly ingested Peruvian bark (also known as cinchona, or quinine), a popular treatment of malaria, he developed the symptoms of the disease. He theorized that if a substance could cause disease symptoms in a healthy person, small amounts could cure an ill one. Using this principle, he sought to identify the healing properties of substances by administering small doses of them to healthy people and observing the symptoms that developed-a process he called proving.
Homeopathy and herbal medicine are both forms of natural medicine and both use herbal extracts, but the mode of preparation, safety profile and indications are different. In addition, homeopathy uses other natural sources such as mineral or animal products, although the majority of the remedies are based on herbs and plants.
The most important difference between homeopathy and herbal medicine is that, unlike herbs, homeopathic remedies are prescribed according to the principle of "similars," or "like cures like." This means that a remedy that treats a certain symptom is the medicine that is able to produce in a healthy individual, the same symptom to that from which the person suffers. The prescription of herbs does not follow the principle of similars.
To understand this concept, consider what happens when you peel an onion. Your most likely responses are tearing and a runny nose, symptoms common in colds. Accordingly, the homeopathic remedy allium cepa, derived from onions (from Allium cepa, onion in Latin) may cure conditions such as colds and allergic reactions and their attendant symptoms. Similarly, bee stings trigger a histamine reaction with localized erythema, edema, and inflammation. Thus, when a person reports heat, redness, and swelling, a homeopath will consider the remedy apis mellifica (after Apis mellifera, or honeybee), derived from the honeybee itself, to treat the discomfort.
Potentization, the process by which a homeopathic remedy is made, was developed by Hahnemann as a means of directly and easily applying the law of similars to healing. The process involves dilution and succussion. First, a substance is placed in alcohol; the resulting extract is called the mother tincture. A drop of this tincture is then sequentially diluted in water and succussed-that is, the container is shaken vigorously and then struck repeatedly against a hard surface. Once the desired concentration is reached, alcohol is again added to the dilution as a preservative and the resulting mixture is sprayed onto sugar pellets. (The alcohol dissipates during the drying of the pellets.)
Hahnemann thought succussion released energy from the extract, which was intensified with subsequent dilutions. Like the law of similars, potentization has ancient origins; proponents believe that it lowers the toxicity of a substance while raising its potency. This premise has been difficult for conventional medical scientists and practitioners to accept. Yet at least one recent study, not related to homeopathy, notes a phenomenon that may elucidate the theories on which homeopathy is based.  Using photographs taken with an electron microscope, the researcher found that when a substance is placed in distilled water, then repeatedly diluted and shaken vigorously, clusters of stable, nonmelting ice crystals formed. These crystals remained undiminished through subsequent dilutions. Therefore, even extremely dilute homeopathic remedies are structurally different from plain water.
Evidence of clinical efficacy of homeopathy
Homoeopathic treatment has been investigated in around 200 clinical trials, and the results of these studies have been subject to systematic review and meta-analysis.
A meta-analysis of data from all placebo-controlled trials of homoeopathy was conducted to assess whether the clinical effect of homoeopathy is equivalent to that of placebo . Overall, 186 trials were identified, 89 of which were eligible for meta-analysis. The results indicated that the effects of homoeopathy are not completely due to placebo; restricting the analysis to high-quality trials only reduced, but did not eliminate, the effect found. However, there was insufficient evidence to demonstrate that homoeopathy is clearly efficacious in any single clinical condition .
Subsequently, a second meta-analysis considered all trials of ‘individualized’ homoeopathy (i.e. where patients are prescribed the remedy most appropriate for their particular symptoms and personal characteristics) . This study pooled the results of 19 placebo-controlled trials and reported that individualized homoeopathy was significantly more effective than placebo. However, when the methodologically best trials only were considered, no effect over that of placebo was seen for homoeopathy. The authors concluded ‘The results of the available randomized trials suggest that individualized homoeopathy has an effect over placebo. The evidence, however, is not convincing because of methodological shortcomings and inconsistencies. Future research should focus on replication of existing promising studies. New randomized studies should be preceded by pilot studies’ . A systematic review of the quality of 59 trials of homoeopathic treatments has provided confirmation of the methodological limitations of these studies .
Further investigations  have explored the impact of study quality on outcome in the trials included in the original meta-analysis . From this work, there was ‘clear evidence’ that studies with better methodological quality tended to yield less positive results, and suggested bias as the most plausible explanation for this . Indeed, there are high-quality trials, published since Linde et al.'s original meta-analysis, reporting negative results [7,8], and it seems likely that the original meta-analysis  ‘at least overestimated the effects of homeopathic treatments’ .
Several other systematic reviews and meta-analyses of controlled trials of homoeopathic remedies have been carried out. Several of these systematic reviews have included all controlled trials of homoeopathy as above, trials of homoeopathic treatments in a single therapeutic condition or area, such as postoperative ileus  or asthma , a specific homoeopathic remedy (such as arnica) in various conditions , or similar homoeopathic treatments in a single condition or similar conditions . Linde et al. summarized this information in a systematic review of systematic reviews, which included 18 such publications . Reports of new well-designed controlled clinical trials of homoeopathic remedies in various clinical conditions continue to be published. Such studies have reported statistically significant  and statistically nonsignificant [15, 16] results for homoeopathic treatment.
One advantage of homeopathy is its purported safety. In order to administer homeopathy effectively, one must match a person's symptoms to a remedy. If the match (also called the simillimum) is correct, the remedy helps stimulate the body's ability to heal. If the match is incorrect, nothing happens.
The safety of homeopathic remedies in part stems from the fact that they are significantly dilute. Remedies are measured according to one of two common scales. The decimal or "x" scale indicates that the dilution is expressed in tenths. The centesimal or "c" scale means that it is expressed in hundredths. Homeopathic dilution has explained as follows: Most remedies are diluted down to "30x," or a strength of 1/10 multiplied by itself 30 times. That means one drop of the active substance is diluted in nine drops of alcohol or water; then a drop of the new solution is further diluted by nine drops, and so on, 30 times. Remember, though, that in homeopathy the more dilute solution is considered more potent. Thus, x potencies are less dilute and less potent than c potencies.
Homeopathic remedies purportedly work by stimulating the body's vital force; they may therefore be more effective for treating illnesses caused by viruses or by antibiotic-resistant organisms than are mainstream medicine drugs, and they do not contribute to the growing problem of antibiotic-resistant bacteria. In a study by Friese and colleagues, the parents of 131 children with acute otitis media were allowed to choose homeopathic or mainstream medicine treatment for their children . Children in the homeopathy group (n = 103) were treated with single remedies including aconitum napellus, apis mellifica, belladonna, chamomilla, and pulsatilla; the children in the allopathy group (n = 28) received nasal drops, antibiotics, and secretolytics and antipyretics. The researchers then evaluated recurrence of infection and found 0.41 recurrences per patient in the homeopathy group versus 0.70 recurrences per patient in the allopathy group. In other words, the children in the allopathy group had nearly double the number of recurrences as did those in the homeopathy group.
Children are an important target group for efforts aimed at reducing unnecessary antibiotic use because they receive a significant proportion of the antibiotics prescribed each year. Nyquist and colleagues studied antibiotic prescribing practices in the United States among children under age 18 who were diagnosed with a cold, an upper respiratory infection, or bronchitis . A total of 531 office visits were evaluated. The researchers found that 44% of children with colds, 46% of those with upper respiratory infections, and 75% of those with bronchitis were prescribed antibiotics, although these conditions typically do not respond to such therapy.