The development of a potentially life-threatening serotonin syndrome (SS) may occur with the use of tramadol products, particularly with concomitant use of serotonergic drugs such as SSRIs, SNRIs, TCAs, MAOIs, and triptans, with drugs which impair metabolism of serotonin (including MAOIs) and with drugs which impair metabolism of tramadol (CYP2D6 and CYP3A4 inhibitors). Here, CYP2D6 is linked to serotonin syndrome.