Switching antidepressants can usually be done within a week if replacing a short half-life antidepressant. However, particular caution is needed if switching:¹²

• From fluoxetine to any alternative as it has a long half-life of about a week
• From fluoxetine or paroxetine to a TCA – the TCA should be started at a lower dose and titrated up as the SSRIs inhibit the metabolism of TCAs
• To a new serotonergic or MAOI as serotonin syndrome is possible
• From a non-reversible MAOI, due to the need for a 2-week flush-out period when no other antidepressant should be prescribed.

When reducing or stopping an antidepressant, NICE recommends the dose be tapered down over four weeks, although this may need longer for short half-life drugs.¹²

Serotonin syndrome is uncommon but potentially serious. It usually arises from taking an SSRI or a serotonin-noradrenaline reuptake inhibitor (SNRI) with another antidepressant or St John’s wort, elevating brain serotonin levels.¹⁴

NICE advises that combining one antidepressant with another, or augmenting with a non-antidepressant drug, should normally only be initiated in primary care by a consultant psychiatrist. This includes the use of lithium, antipsychotics such as aripiprazole, olanzapine, quetiapine or risperidone, or other antidepressants such as mirtazapine or mianserin. There should be regular monitoring if lithium or an antipsychotic is co-prescribed.¹²

Useful Resources 

·       Centre for Mental Health

·       College of Mental Health Pharmacy (CMHP)

·       Mental Health Foundation

·       NHS Adult Improving Access to Psychological Therapies programme

·       NHS Digital Mental health data hub

·       NHS Mental Health