Serotonin Syndrome Presenting with Concomitant Tramadol and Diphenhydramine Use: A Case Report of an Unlikely Side-Effect.

Serotonin syndrome is a condition that occurs following the administration of serotonergic drugs. Interestingly, on rare occasions, it can occur with various drug combinations that can secondarily affect the serum levels of 5-hydroxytryptamin. Tramadol is an analgesic that has mu opioid receptor agonist activity and has also been shown to inhibit the reuptake of serotonin and noradrenaline.