side effects may result from interactions with other medications. Tramadol has the same dose-dependent adverse effects as morphine including respiratory depression. Dependence and withdrawal Long-term use of high doses of tramadol causes physical dependence and withdrawal syndrome. These include both symptoms typical of opioid withdrawal and those associated with serotonin–norepinephrine reuptake inhibitor (SNRI) withdrawal; symptoms include numbness, tingling, paresthesia, and tinnitus. Psychiatric symptoms may include hallucinations, paranoia, extreme anxiety, panic attacks, and confusion. In most cases, tramadol withdrawal will set in 12–20 hours after the last dose, but this can vary. Tramadol withdrawal typically lasts longer than that of other opioids. Seven days or more of acute withdrawal symptoms can occur as opposed to typically 3 or 4 days for other codeine analogues. Overdose Recognised risk factors for tramadol overdose include respiratory depression, addiction, and seizures. Naloxone only partially reverses the toxic effects of tramadol overdose and may increase the risk of seizures. Deaths with tramadol overdose have been reported and are increasing in frequency in Northern Ireland; the majority of these overdoses involve other drugs including alcohol. There were 254 tramadol-related deaths in England and Wales in 2013, and 379 in Florida in 2011. In 2011, 21,649 emergency room visits in the United States were related to tramadol. Interactions Tramadol can interact with other medications with similar mechanisms of action. Tramadol acts as a serotonin-norephinephrine reuptake inhibitor and thus can interact with other serotonergic medications (selective serotonin reuptake inhibitors, serotonin–norepinephrine reuptake inhibitors, tricyclic antidepressants, triptans, cough and cold medications containing dextromethorphan, herbal products containing St. John’s wort, and medications that inhibit the metabolism of serotonin, such as monoamine oxidase inhibitors) and, in combination, may lead to serotonin syndrome. It may also make some serotonergic antagonist anti-emetic medications (ondansetron) less effective. Tramadol also acts as an opioid agonist and thus can increase the risk for side effects when used with other opioid analgesics (such as morphine, pethidine, tapentadol, oxycodone, and fentanyl). Tramadol is metabolized by CYP2D6 enzymes which contribute to the metabolism of approximately 25% of all medications. Any medications with the ability to inhibit or induce these enzymes may interact with tramadol. Tramadol increases the risk for seizures by lowering the seizure threshold. Using other medications that lower seizure threshold (such as antipsychotic medications or amphetamines), further increases this risk. Pharmacology Mechanism of action Tramadol induces analgesic effects through a variety of different targets on the noradrenergic system, serotoninergic