Tasimelteon, developed by Vanda Pharmaceuticals Inc under license from 
Bristol-Myers Squibb Co, is a melatonin receptor agonist. Because of the high 
density of melatonin receptors in the circadian pacemaker, the suprachiasmatic 
nucleus, melatonergic actions can phase-shift circadian rhythms and promote 
sleep. Tasimelteon was effective in reducing sleep onset latency (in phase II 
and III clinical trials) and in resetting the circadian melatonin rhythm (in 
phase II trials), which indicated its potential suitability as treatment for jet 
lag, shift work and circadian rhythm sleep disorders. Statistically significant 
improvements in sleep maintenance have also been observed with the drug. 
Tasimelteon has been claimed to be useful in the treatment of depression, and 
preclinical evidence in this respect is to be confirmed in a phase II clinical 
trial, which was ready to be initiated at the time of publication. It is 
plausible that the drug may be effective in the treatment of depressive 
disorders, at least those that are related to circadian dysfunction, and that it 
may attenuate sleep problems in depressed patients of different subtypes. A 
general suitability in mitigating other symptoms of major depressive disorder 
cannot be deduced from the actions of tasimelteon via the melatonin receptors 
MT1 and MT2. The drug is well tolerated, does not induce impairment of next-day 
functioning or dependence, and seems to be safe in short-term treatment; 
however, toxicological data would be required for assessing its long-term 
safety.