TriCyclic or TetraCyclic Antidepressants are the most frequently described class of antidepressant and are used for the most common form of serious depression.
An example of is Imipramine, commercial name of Tofranil. The mechanism of action of imipramine HCl is not definitely known. However, it does not act primarily by stimulation of the central nervous system.
The main disadvantages of these class of drugs are that they take 2-5 weeks to become effective and they can cause side effects such as over sedation and cardiac problems.