**6. Side effects and clinical/paraclinical findings**

Tramadol is an analgesic with less side effects in comparison with other opioids [64]. It has the least gastrointestinal and renal toxicities [65]. Drug screening for opioids is generally negative in the patients with tramadol overdose [66].

In overdose, lethargy, nausea, tachycardia, agitation, seizure, coma, hypotension, hyperten‐ sion, respiratory depression, dysuria, constipation, dizziness, facial paresthesia, ataxia, headache, edema, movement disorders, perspiration, blurred vision, hallucination, itching, vertigo, palpitation, hypo- and hyper-reflexia, diplopia, multi-organ failure, acute liver failure due to fulminant liver necrosis, renal failure, and urine retention have been reported [8,17,23, 48-51,64,67,68]. Dizziness, nausea, constipation, vertigo, and headache are the most common symptoms [57,69,70]. Miosis is not as common as that in toxicities with other opioids and is detected in up to one-thirds of the patients probably due to serotonin and norepinephrine reuptake inhibition [71].
