There are a number of biological molecules which are involved in a bewildering amount of activities. Serotonin is one. First thought to have the sole potential of contracting blood vessels, over the years serotonin has demonstrated that there is more to it than meets its chemistry. Besides its vasoconstrictor properties, it is also believed to be involved in instances as diverse as embryonic development, mood, appetite, nausea, sleep, body temperature, ageing, premature ejaculation, pain, anxiety, aggression, memory, cognition and migraines. And no doubt, as time goes by â€“ as it inevitably does â€“ yet more activities will be added to serotoninâ€™s already impressive panoply. It is hardly surprising, then, that serotonin has been shown to play a part in psychiatric shortcomings such as obsessive compulsive disorder and impulsivity. But serotonin cannot do this by itself; it needs a receptor to which it can bind. A receptor known as the 5-HT receptor.