Groups of Antidepressants and How They Work

Tricyclics (TCAs)
The tricyclic group of antidepressants – named for the three rings making up the chemical shape of the drug – act by blocking the reuptake of norepinephrine back into the sending cell, so there are more NTs in the gap to combat depression. Commonly prescribed drugs from this group include imipramine, amitriptyline, clomipramine, and newer compounds that have a quicker onset of action and fewer side effects, such as nortriptyline and desipramine. The doctor may need to increase the dosage of the drug until you get the full benefit.

Tricyclics have many possible side effects. Some of the more unwelcome ones are weight gain, drowsiness, constipation, dry mouth, blurred vision, dizziness and a decrease in blood pressure. You must move very slowly from lying down to sitting up to standing, so that your blood pressure can adjust to the change in posture; otherwise, you may faint. If you suffer from glaucoma (elevated pressure within the eyes) or heart problems, you may not be able to take these drugs. An overdose of tricyclics can be deadly.

Tricyclics work particularly well in depressed adult men, in severe depressions with many physical symptoms, and in depressions marked by excessive fatigue and lethargy. They are less often used in the young and the elderly because they slow the conduction time of the heart, increase the heart rate, and cause a lowering of the blood pressure.
Antidepressants Tricyclic

Overdoses of small amounts of tricyclic antidepressants can be lethal particularly when combined with other mood altering substances such as alcohol. They can also be very risky in patients with major mental disorders such as schizophrenia and mania because of the risk of suicide. In bipolar patients, manic episodes can be started after taking any antidepressant.

Newer antidepressants are safer in overdoses and just as effective.

Monoamine Oxidase Inhibitors (MAOIs)
Monoamine oxidase inhibitors work by irreversibly changing the enzyme, monoamine oxidase, that breaks down NTs, so that amounts of both norepinephrine and serotonin increase in the synapses. Drugs in this group include phenelzine and tranylcypromine. These drugs are now used less frequently than in the past because they can be quite dangerous. They cannot be used with other antidepressants.

They cause the ‘cheese reaction’, a hypertensive (high blood pressure) crisis, when combined with certain foods – ripe cheeses, beer, liqueurs, offal, smoked meats, smoked fish, soy sauce, teriyaki, tofu, sauerkraut, fava beans, avocados, dried figs, caviar, yeast extracts such as Marmite and Bovril. These foods contain large amounts of the amino acid tyramine.

MAOIs also interact with off-the-shelf nasal sprays, cough medicines, and weight-control preparations containing ephedrine, and with other antidepressants such as the tricyclics and the selective serotonin reuptake inhibitors. If monoamine oxidase is irreversibly changed, the amino acid tyramine makes more and more norepinephrine, and there is no longer monoamine oxidase to inactivate it – or to inactivate ephedrine, which is very similar in action to norepinephrine. Eventually the level of norepinephrine becomes high enough to raise the blood pressure to the point where it causes a splitting headache or even a stroke. This is obviously a medical emergency. (Needless to say, your doctor would have to be certain you were not suicidal when using such a high-risk drug.) Some doctors even suggest you carry an antidote, phentolamine, in case you have a sudden rise in blood pressure from a cheese reaction. In any case, if you have the reaction, you should go to the nearest A & E department at once.

Groups of Antidepressants and How They Work
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