This is an older group of antidepressants, which is used less frequently today. These agents act by inhibiting an enzyme called monoamine oxidase which usually breaks down serotonin, noradrenaline and dopamine in the brain. This results in an increase in these neurotransmitters, the deficiency of which is associated with depressive illness.

However, certain foodstuffs containing tyramine (e.g. cheese, red wine, processed meats and many others) also require monoamine oxidase for their metabolism. The inhibition of this enzyme results in an excess of tyramine which acts upon the blood vessels to cause a rise in blood pressure. This rise may sometimes be fatal and hence patients taking MAOI’s need to observe dietary restrictions.

The danger of any food or drug reaction persists for about 14 days after stopping treatment with a MAOI. A washout period is therefore required before starting a different antidepressant.

The only MAOI as described above that is available in South Africa is Parnate (Tranylcypromine). There is a newer MAOI available, which does not completely inhibit the monoamine oxidase enzyme and dietary restrictions are thus not that important. A severe hypertensive episode is much less likely and these drugs are only contra-indicated if the patient already suffers from uncontrolled high blood pressure. This drug is called Aurorix (Moclobemide).

MAOI’s are thought to be particularly useful in treating atypical depression. They are also useful when depression is not responding to other drugs and in phobia and panic disorder.

Common side-effects include:

 
• headache - may be a warning sign of a severe increase in blood pressure;  
• dizziness;  
• agitation/nervousness;  
• insomnia;  
• sexual problems;  
• drug interactions;  
• interactions with certain foods

Again most of these side effects usually improve after taking the medication for a few weeks.