The first antidepressant drugs appeared in pharmacies about 50 years ago and were monoamine oxidase inhibitors and tricyclic antidepressants, which were discovered through clinical trials and were effective; they achieved their purpose by improving the mechanisms of the noradrenergic system and the serotonergic system. Unfortunately, they all carried undesirable side effects such as drowsiness, dizziness, and dry throat. 

The new generation of antidepressants includes:

• multiple-receptor antidepressants
• Single-receptor selective serotonin reuptake inhibitors.

These antidepressants have the characteristic of not activating unwanted effects because they stimulate neither acetylcholine nor histamine.