In the late 1950s, the first antidepressant, imipramine, was identified. At almost the same time, iproniazide, a drug used to treat tuberculosis, was found to have antidepressant properties. After these two drugs were discovered, other antidepressants were developed that had fewer side effects, more sedation, quicker onset of action, and other preferable characteristics. Research continues to come up with faster-acting and better antidepressants. The drugs are used for depression, and are also used – combined with mood-stabilizing drugs – for the depression phase of bipolar disorder.
In treating depression, we want to increase the level of NTs in the synapse (gap). How can we do that? It’s a complicated process, but if you have a basic understanding of how it works, the different groups of antidepressants will be much easier to understand.In cells on the ‘sending’ side of the synapse, enzymes convert certain molecules into the NTs epinephrine and serotonin. These are released into the synapses to do their ‘messenger’ work. But they don’t remain active indefinitely. They are deactivated in one of two ways: either they are taken back (reuptake) into the ‘sending’ cells and deactivated there, or an enzyme called monoamine oxidase (MAO) deactivates them within the synapse. They are eventually metabolized, or broken down, by the liver and kidneys. By slowing down the deactiva¬tion of NTs while new ones are being created, we can increase the level of NTs in the synapses at any given time.
We use various groups of drugs to slow down the decrease of NTs in specific ways. We can inhibit (block) the reuptake of NTs by the sending cells, by using drugs that fool the body. We can inhibit the breakdown action of the MAO. Or, if we want to stop the action of some receptors but not others – for example, if we want to block depression without causing nausea or sexual dysfunction – we can use an antagonist to target specific receptors. Thus, a drug described as a serotonin-2 antagonistlreuptake inhibitor stops the action of the number-2 receptors in the receiving cells, while also blocking the deactivation of the serotonin so that it remains active longer.
These are generic names of some drugs used to treat depression
- Tricyclic antidepressants: imipramine, amitriptyline, clomipramine, nortriptline, desipramine.
- Monoamine oxidase inhibitors: phenelzine, tranylcypromine, iproniazide
- Reversible inhibitors of monoamine oxidase: moclobemide