Serotonin is a neurotransmitter, meaning that it travels between neurons in the brain to relay chemical messages. When neurons communicate they release serotonin into the space between neurons called the synapse. After the serotonin has delivered its message, the neuron sending the serotonin reabsorbs the chemical. Besides working as a chemical messenger, serotonin seems to sooth the mind. Antidepressant drugs such as Prozac work by causing serotonin to remain in the synapses longer before being reabsorbed, thus having an even greater calming effect.

Several studies have linked suicide to low levels of serotonin in the brain. Scientists have determined that the brains of at least some suicide victims had tried to horde serotonin by not allowing it to be reabsorbed into the synapse. While low serotonin levels alone do not cause someone to commit suicide, they seem to play an important role.

Although lithium in pill form is a proven suicide deterrent, many at-risk patients shun the drug due to side effects including hand tremors, thirst, and weight gain.