The most prescribed drugs in many parts of the world are drugs which alter serotonin levels. They are used in depression, generalized anxiety disorder and social phobia. The MAOIs prevent the breakdown of monoamine neurotransmitters (including serotonin), and therefore increase concentrations of the neurotransmitter in the brain. MAOI therapy is associated with many adverse drug reactions, and patients are at risk of hypertensive emergency triggered by foods with high tyramine content and certain drugs. Some drugs inhibit the re-uptake of serotonin, making it stay in the synapse longer. The tricyclic antidepressants (TCAs) inhibit the re-uptake of both serotonin and norepinephrine. The newer selective serotonin re-uptake inhibitors (SSRIs) have fewer side-effects and fewer interactions with other drugs. The side effects that have become apparent in recent times include a decrease in bone mass in elderly and increased risk for osteoporosis. However, it is not yet clear whether it is due to SSRI action on peripheral serotonin production and or action in the gut or in the brain.[37] Certain SSRI medications have been shown to lower serotonin levels below the baseline after chronic use, despite initial increases in serotonin. This has been connected to the observation that the benefit of SSRI's may decrease in selected patients after a long-term treatment. A switch in medication will usually resolve this issue (up to 70% of the time).[66] The novel antidepressant tianeptine, a selective serotonin reuptake enhancer, has mood-elevating effects. This provides evidence for the theory that serotonin is most likely used to regulate the extent or intensity of moods, rather than level directly correlating with mood.
Although phobias and depression might be attenuated by serotonin-altering-drugs this does not mean that the individual's situation has been improved, but only the individual's perception of the environment. Sometimes a lower serotonin level might be beneficial, for example in the ultimatum game, where players with normal serotonin levels are more prone to accept unfair offers than participants whose serotonin levels have been artificially lowered.[67]
