Tricyclic antidepressants (TCAs) can be used to treat symptoms of depression, as well as other mental illnesses. They are named as such as they have 3 rings in their chemical structure. The exact cause of depression is unknown but it has been suggested that it is caused by a lack of monoamine neurotransmitters, 5-HT (serotonin) and noradrenaline, in the brain. Tricyclic antidepressants work by inhibiting the reuptake of these neurotransmitters, meaning that there is more available in the synapse and therefore increased transmission.
Other forms of antidepressants are now used instead which have fewer side effects and less toxicity, TCAs can have side effects such as a dry mouth, sedation and postural hypotension (a drop in blood pressure when standing up).