The combination should be avoided. • Caution should be exercised in patients on 5- or 8-methoxypsoralen (5 and 8-MOP), which increases melatonin levels by inhibiting its metabolism. • Caution should be exercised in patients on cimetidine a CYP2D inhibitor, which increases plasma melatonin levels, by inhibiting its metabolism. • Cigarette smoking may decrease melantonin levels due to induction of CYP1A2. • Caution should be exercised in patients on oestrogens (e. g. contraceptive or hormone replacement therapy), which increase melatonin levels by inhibiting its metabolism by CYP1A1 and CYP1A2. • CYP1A2 inhibitors such as quinolones may give rise to increased melatonin exposure. • CYP1A2 inducers such as carbamazepine and rifampicin may give rise to reduced plasma concentrations of melatonin. • There is a large amount of data in the literature regarding the effect of adrenergic agonists/ antagonists, opiate agonists/ antagonists, antidepressant medicinal products, prostaglandin inhibitors, benzodiazepines, tryptophan and alcohol, on endogenous melatonin secretion.