Interaction of Fluoxetine and Caffeine in a Patient With Substance-Induced Mania

Substance-induced manic episodes may occur in individuals without prior psychiatric illness and can be triggered by medications or stimulants. Selective serotonin reuptake inhibitors (SSRIs) and high caffeine intake have both been associated with mood destabilization.

To describe a case of acute mania potentially precipitated by excessive fluoxetine use and high caffeine consumption.

A 42-year-old male with no prior psychiatric history presented with symptoms of acute mania after recently starting fluoxetine and accidentally taking approximately twice the prescribed dose. Clinical evaluation, laboratory testing, urine drug screening, and collateral history were obtained.

The patient exhibited elevated mood, grandiosity, pressured speech, and decreased need for sleep. Laboratory results were unremarkable except for cannabis on urine drug screening. Fluoxetine was discontinued, and he was treated with valproate and adjunctive haloperidol during inpatient hospitalization, leading to improvement in symptoms.

The manic episode may have been triggered by excessive fluoxetine exposure combined with high caffeine intake. Fluoxetine may also inhibit CYP1A2, potentially increasing caffeine levels and amplifying stimulant effects.

This case highlights a possible interaction between fluoxetine and caffeine contributing to mania and underscores the importance of assessing stimulant use and medication dosing when evaluating new-onset manic symptoms.