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Quinine has been used for the treatment of malaria and muscle cramps for centuries and has been available in an artificially synthesised form for over 50 years. Muscle cramps are sudden episodes of painful muscle contraction that may last for seconds to minutes and vary in frequency and severity from person to person. Most happen at night in leg muscles, but any muscle may be affected at any time. Most cramps occur for unknown reasons, but diseases of nerves, kidney diseases, pregnancy and disturbances of blood salt levels may increase their occurrence.

Doses of 200–300 mg of quinine sulphate once per day have commonly been prescribed for the treatment of cramps in cramp sufferers. In our Cochrane review of the scientific evidence on its effects, we sought to identify and analyse the high quality evidence and to present the data for both its benefits and harms (1). This thorough review identified a total of 23 trials with nearly 1600 participants and is the most comprehensive, systematic study of quinine's effectiveness to date. Some of the studies for which we obtained data have not been published, but the results of these studies are important in providing a complete picture about the drug.

When compared to a placebo dummy drug, quinine in doses of 200 to 500mg per day reduced leg cramps by over a quarter, the number of days on which cramp occurred by one fifth and the intensity of cramps by one tenth. This direct evidence of benefit came from 13 scientific studies including almost 1000 patients, and was judged to be of moderate quality. Some studies compared quinine to vitamin E, or to a combination of quinine and a caffeine-like stimulant called theophylline, but we found no high quality evidence that these therapies provide any significant or additional benefit.

Concerns have been raised about the safety of quinine, which led to its withdrawal as a treatment of cramps from the US market in 2006. In the highest quality studies which we were able to include, we found that minor side effects such as tummy upset were reported for about 3% more patients taking quinine than placebo. However, a serious side effect occurred in only a single patient, who recovered on stopping the drug. Although the number of patients in these combined studies is relatively small and side effects were not specifically sought in all the studies, we conclude that these harms are relatively uncommon.

Therefore, having looked through decades of research, we’ve found that there is moderately high quality evidence which shows that quinine is both effective and relatively safe for the treatment of muscle cramp, but further surveillance is required to judge the true incidence of rare side effects.