This study is a review of the pain relieving (analgesic) effects of melatonin, a hormone produced by the pineal gland. This hormone is known to reduce blood pressure, enhance sleep, reduce anxiety and destroy harmful oxidants in the body. Experiments on rats have shown that melatonin increases the pain threshold, while clinical trials in humans suggest that patients suffering from fibromyalgia, irritable bowel syndrome or migraines have found considerable relief from pain through melatonin therapy. This review evaluates the available evidence on the analgesic properties exhibited by the melatonin hormone present in animals and humans.
In present day therapeutics, non-steroidal anti-inflammatory drugs (NSAIDs) and morphine are two important agents used for decreasing pain. Though these drugs are effective painkillers, they are also known to cause severe side effects. NSAIDs cause gastritis, leading to damage in the stomach and duodenum, and sometimes increase bleeding from wounds. Morphine often causes constipation, sedation and sleep disturbances. Moreover, its long-term use by a patient may induce addiction to this drug. Hence, scientists are in constant search of a novel pain killer devoid of these side effects. Melatonin appears to be a potential alternative for the currently used analgesics. The authors of this review investigated the available literature on the study of the analgesic effects of melatonin. They focused on clinical trials of three important diseases — fibromyalgia, irritable bowel syndrome and migraine.
The reviewers first evaluated studies done on rats to investigate the analgesic effects of melatonin. In almost all the experiments, melatonin was injected into rats, and their capacity to tolerate or sense pain was measured. The results were compared with those in whom melatonin was not administered. Various methods such as electric stimulation, heat application, chemical injection into the skin and clamping of tail were used to induce pain in rats. Experiments in humans involved measurement of melatonin levels in patients and their comparison with those obtained from healthy individuals. Finally, experiments done for finding out the side effects of melatonin were also reviewed.
* Rats, in whom melatonin was administered, tolerated the pain well. These rats showed withdrawal movements such as retrieval of paws and raising the tail, after a much longer time than rats in the control group. A significant effect was seen when melatonin was given in a dose of more than 25 mg per kilogram of body weight.
* In human clinical trials, melatonin levels in blood were found to be high in some studies and low in others. Treatment with melatonin, especially when combined with fluoxetine, provided a lot of relief to patients suffering from fibromyalgia.
* In irritable bowel syndrome, levels of melatonin in saliva were low, and administration of 3 mg of oral melatonin reduced pain in these patients. Urinary concentrations of melatonin were high in patients with migraine. Melatonin infusion reduced headache. Moreover, patients who received prophylaxis using melatonin had reduced frequency and less severity of migraine attacks.
* Studies done to identify toxic effects of melatonin were unsuccessful in finding any adverse effects.
Although this review successfully highlights the analgesic effects of melatonin, there is still a need for identification of the mechanism involved in it. Some studies have proposed that melatonin binds to the same receptors in the brain to which morphine binds. But this hypothesis has to be confirmed by experimental studies.
The analgesic effects of melatonin are very well documented in the present review. Melatonin has been found to be useful in reducing pain in patients suffering from fibromyalgia, irritable bowel syndrome and migraine. This hormone, being free of any serious adverse effects, can be used safely in the treatment of all these diseases. Melatonin, in addition to its analgesic effects, has the capacity to reduce anxiety and induce sound sleep. These effects may further enhance the comfort of the patients. With pain being the most common symptom of all medical conditions, identification of a novel analgesic drug such as melatonin may prove to be a milestone invention in the field of medicine.
For More Information:
Analgesic Effects of Melatonin: A Review of Current Evidence from Experimental and Clinical Studies
Publication Journal: Journal of Pineal Research, April 2011
By Michael Wilhelmsen; Ilda Amirian; University of Copenhagen, Herlev, Denmark
*FYI Living Lab Reports Are Summaries of the Original Research.