Millions of US patients with insomnia could have access to a novel treatment option following the launch of Merck & Co’s Belsomra (suvorexant) this week.

The drug is the only orexin receptor antagonist approved for the treatment of insomnia in the country. This new class of medicines works by blocking the action of orexin - one of many neurotransmitters involved in promoting wakefulness - to suppress the wake drive in the brain.

US Food and Drug Administration approval for Belsomra in 5mg, 10mg, 15mg and 20mg strengths was issued in August last year, but higher doses were rejected on safety concerns. 

On the safety side, the drug is classed a Schedule IV controlled substance because it can be abused or lead to independence. It is also contraindicated in patients with narcolepsy, and carries warnings of its potential to impair daytime wakefulness and that central nervous system depressant effects can last for up to several days after discontinuation. 

Like other sleep medicines, there is a risk from Belsomra of sleep-driving and other complex behaviours while not being fully awake, such as preparing and eating food, making phone calls, or having sex. Chances of such activity increase if a person has consumed alcohol or taken other medicines that make them sleepy, the FDA noted.