What is serotonin?

Serotonin, or 5-hydroxytryptamine, is made from the amino acid tryptophan. Although famous as a brain chemical, around 90 percent of the body’s serotonin is produced in the gut, where it helps control digestion. In the brain it acts as a neurotransmitter affecting mood, appetite, sleep and memory, and it is used to make melatonin. Many antidepressants, called SSRIs, work by increasing serotonin available between nerve cells. Scientists now consider the old idea that depression is simply a “serotonin imbalance” to be an oversimplification.