The MAOIs are notorious for their many interactions with other foods. This occurs through inhibition of tyramine metabolism, but moclobemide's reversible inhibition of MAO allows ingested tyramine to be metabolised and it is therefore much better tolerated. Also to its advantage, unlike other MAOIs, moclobemide prolongs sleep with REM suppression, and does not cause sexual dysfunction. It does not precipitate seizures or modify psychomotor performance and so is safer to use with epileptic patients. SSRI-related side effects are most prominent at the start of treatment and those most commonly reported are nausea, insomnia and anxiety.
Sexual dysfunction is also common and often leads to non-compliance.
However, unlike the other groups the SSRIs do not cause weight gain. This is because SSRIs inhibit a number of hepatic cytochrome p450 enzymes and so can increase the blood levels of other drugs metabolised by the same enzymes, such as the tricyclics. When prescribed with MAOIs, SSRIs can cause the serotonergic syndrome, in which there is a marked increase in blood pressure. Caution should be exercised when switching these classes. Novel antidepressants cannot be placed in any of the above groups because of their unique pharmacology and mechanism of action.