While serotoninergic Syndrome is discussed a lot, there are surprisingly few cases reported in the literature.  SSRI anti-depressants alone or in combination with other anti-depressants make up most of the cases.  The rarity of the syndrome is good, since it is potentially fatal.  Symptoms may include confusion, agitation, myoclonus, diaphoresis, tremor, hyperreflexia, fever, weakness, nausea, and diarrhea.  The confusion, myoclonus, and tremor are especially common.

Cyproheptadine: Diagnosis Serotonin Syndrome: Rapid reversal of mydriasis in serotonin syndrome by cyproheptadine may serve as a specific suppressive test for the condition, and possibly may add to our understanding of the syndrome. Treatment with cyproheptadine is not thought to abbreviate the illness, but provides symptomatic relief while symptoms persist. Ann Pharmacother 2001 Jul-Aug;35(7-8):870-3

Cyproheptidine: Serotonin Syndrome Treated: The serotonin syndrome is the result of excess stimulation of central nervous 5-hydroxytryptamine (5HT)-1a and 5HT-2 receptors. The diagnosis requires a history of exposure to agents active at serotonin receptors and the presence of alterations in mental status, autonomic instability, and neuromuscular abnormalities such as tremor, hyperreflexia, or myoclonus. In this descriptive case series, five cases of serotonin syndrome are reported. All patients gave a history of recent exposure to one or more serotonergic medications, including moclobemide, paroxetine, sertraline, and venlafaxine, with clinical evidence of serotonin syndrome. All patients were administered cyproheptadine (4-8 mg orally) for serotonergic signs. Three had complete resolution of signs within 2 h of administration. Another two had a residual tremor or hyperreflexia following the first dose, which resolved following a repeat dose. There were no adverse outcomes. Treatment of the serotonin syndrome with cyproheptadine. Graudins A, Stearman A, Chan B. J Emerg Med 1998 Jul-Aug;16(4):615-9

Sertraline Serotoninergis Syndrome Followed by Citalopram Repeat: In a case report of a serotonin syndrome (SS) in a 64-year-old depressed female patient with alcoholic hepatic cirrhosis after treatment with an increase in dosage of sertraline. After improvement, the therapy with citalopram led again to development of milder SS, this time immediately after the increase of the dosage. Repetition of serotonin syndrome after reexposure to SSRI--a case report. Tomaselli G, et al. Pharmacopsychiatry 2004 Sep;37(5):236-8.

Paroxetine/Tramadol Sertotonin Syndrome: Two elderly with major depression were treated with paroxetine with tramadol for bone pain.  SS symptoms were nausea, diaphoresis, irritable, weak, confused, fever, agitation, restless. Patients stopped both medications and got better. Cyproheptadine (serotonin receptor antagonist) also used for one. Tramadol (Ultram) analgesic that inhibits reuptake of serotonin and norepinephrine. Internatl J Ger Psych 98;13:343

Paroxetine/Buspirone/Papaverine: A case report of a 52 year old woman on buspirone prescribed paroxetine and papaverine, who within a month she experienced high fever, shivering, tremor, hyper-reflexia, tachycardia (120 bpm), and tracheal cramps. Both paroxetine and buspirone have serotonergic effects. She also had ecchymoses on her thighs, probably due to serotonergic effects. The symptoms rapidly decreased after withdrawing paroxetine. Paroxetine, papaverine, and possibly also buspirone interact with cytochrome P450 CYP2D6. They can probably inhibit the metabolism of each other. Combination of serotonergic agents resulted in severe adverse effects. Jagestedt M, et al. Lakartidningen 2004 Apr 29;101(18):1618-9.

Selegiline Can Cause a Serotoninergic Syndrome and Hypertension, so must not be combined with pethidine, tramadol, bupropion, sumatriptan, zolmitriptan or naratriptan. Concurrent treatment with serotonin reuptake inhibitor antidepressants should also be avoided. Authors say too dangerous for Parkinson's. Prescrire Int 2002 Aug;11(60):108-11.

Four Cases While Switching MAOIs to Venlafaxine: Four pts being treated for headaches. Serotonin syndrome induced by transitioning from phenelzine to venlafaxine: four patient reports. Diamond S, Pepper BJ, Diamond ML, Freitag FG, Urban GJ, Erdemoglu AK. Neurology 1998 Jul;51(1):274-6

Fluoxetine to Venlafaxine Case: 39-year-old white woman with depression and panic attacks was being treated with fluoxetine, trazodone, clonazepam, and cimetidine. After fluoxetine and clonazepam were abruptly discontinued, venlafaxine and lorazepam were started. Within 24 hours, she developed diaphoresis, tremors, slurred speech, myoclonus, restlessness, impaired thinking, and diarrhea. This constellation meets Sternbach's criteria for serotonin syndrome. USD, Sioux Falls. Serotonin syndrome induced by venlafaxine and fluoxetine: a case study in polypharmacy and potential pharmacodynamic and pharmacokinetic mechanisms. Bhatara VS, Magnus RD, Paul KL, Preskorn SH. Ann Pharmacother 1998 Apr;32(4):432-6

A case of Serotonin Syndrome caused by Venlafaxine and Lithium: Mekler G, Woggon B. Pharmacopsychiatry 1997 Nov;30(6):272-3

Clomipramine: Some Symptoms Frequent: Tremor & Myoclonus: The serotonin syndrome includes confusion, agitation, myoclonus, diaphoresis, tremor and diarrhea. The authors evaluated 38 depressed inpatients treated with clomipramine. Sixteen (42%) patients presented at least one symptom. In 14 cases tremor and myoclonus occurred simultaneously, and 10 patients presented at the same time tremor plus myoclonus, diaphoresis and shivering. Except for 2 patients, symptoms were transient, lasted less than 1 week and disappeared with the pursuit of treatment. Prospective evaluation of the serotonin syndrome in depressed inpatients treated with clomipramine. Lejoyeux M, et al. Colombes, France. Acta Psychiatr Scand 1993 Nov;88(5):369-71.