Depersonalisation/derealisation (DD) syndrome is often associated with severe traumatic experiences and the use of certain medications. Our patient reported experiencing a transient DD phenomenon a few hours after taking 37.5 mg of tramadol, together with etoricoxib, acetaminophen and eperisone. His symptoms subsided upon tramadol discontinuation, suggesting the possibility of tramadol-induced DD. A study of the patient’s cytochrome P450 (CYP) 2D6 polymorphism, which mainly metabolises tramadol, indicated normal metaboliser status with reduced function. The concomitant administration of the CYP2D6 inhibitor, etoricoxib, would have led to higher concentrations of the serotonergic parent tramadol, providing an explanation for the patient’s symptoms.