SSRI, SNRI and mirtazapine drug contraindications include monoamine oxidase inhibitors (MAOIs) and a flush out period is required if a patient is swapping from an MAOI to another antidepressant, and vice versa. Concomitant use of the antipsychotic pimozide is also contraindicated, while concomitant use of St John’s Wort preparations should be avoided.¹¹

Other contraindications include where heart rhythm problems (prolonged QT interval) exist, whether due to disease or other medication. Examples of common drugs associated with prolonging QT intervals include amiodarone, citalopram, erythromycin, clarithromycin, tamoxifen, ondansetron, and fluconazole, but there are many others.^11,18

Factors increasing QT risk include:¹⁸

·       electrolyte imbalance (eg vomiting, chronic diarrhoea, laxative abuse)

·       inhibiting medicines breakdown by blocking CYP3A4 enzymes (eg erythromycin)

·       additive QT effects (eg domperidone for nausea/vomiting when already taking citalopram).

Fluoxetine is contraindicated in combination with metoprolol used in cardiac failure. Mirtazapine may need close monitoring in patients with hypotension.¹¹