early 1950s it was confirmed that both substances were the same. In the mid-1950s it was proposed that serotonin had a role as a neurotransmitter in the central nervous system (CNS) of animals. Investigations of the mechanism of action were not very successful as experimental techniques were lacking. Later in the 1960s, studies showed that vasoconstriction caused by 5-HT, noradrenaline and ergotamine could reduce migraine attacks. Patrick P.A. Humphrey among others at Glaxo started researching the 5-HT receptor to discover a more direct 5-HT agonist with fewer side effects. They continued developing and working on a desirable action on 5-HT by 5-HT1 receptor activation for an anti-migraine drug. Continued work led to the development of sumatriptan, now known as the first 5-HT1 agonist, selective for the 5-HT1D/B receptors and also the 5-HT1F receptor with less affinity. By 1991 sumatriptan became available in clinical use in the Netherlands and in the US in 1993. However, there was always a debate about its mechanism of action, and it still remains unclear today. Later, Mike Moskowitz proposed a theory about "neuronal extravasation", and this was the first clue that sumatriptan might have a direct neuronal effect in migraine attacks. Sumatriptan became a prototype for other triptans that have been developed for improved selectivity for the 5-HT1D/B receptors. Society and culture Legal status These drugs have been available only by prescription (US, Canada and UK), but sumatriptan became available over-the-counter in the UK in June 2006. The brand name of the OTC product in the UK is Imigran Recovery. The patent on Imitrex STATDose expired in December 2006, and injectable sumatriptan became available as a generic formula in August 2008. Sumavel Dosepro is a needle-free delivery of injectable sumatriptan that was approved in the US by the FDA in July 2009. Sumatriptan became available as a generic in the US in late 2009. It used to be sold over-the-counter in Romania under the Imigran brand; however, as of August 2014 prescription is required. Zecuity, a sumatriptan transdermal patch, was approved by the US FDA in January 2013. The sumatriptan nasal powder was approved by the FDA in January 2016 and became available in the U.S. May 2016. Naratriptan is available OTC in Germany and Brazil. References Notes Sources 5-HT1D agonists Migraine