Compare conditions

Put any two — or three — conditions side by side, adult or pediatric, to spot the look-alike differences fast, row by row.

Serotonin Syndrome

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In one line

·Taking two drugs that both raise serotonin (like an SSRI plus an MAOI, linezolid, tramadol, methylene blue, or MDMA) floods the brain with too much serotonin and poisons the nervous system.

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Normal physiology

·Normally the brain keeps serotonin—a messenger chemical—at a steady, balanced level so mood stays even, thinking stays clear, body temperature stays normal, and muscles move smoothly without shaking or locking up.

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What goes wrong

·When you take two drugs that both raise serotonin—like an SSRI (which blocks the pump that sucks serotonin back in) plus an MAOI (which blocks the enzyme that breaks serotonin down)—the serotonin piles up with nowhere to go, flooding every receptor and locking the brain's alert and movement circuits wide open.

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Hallmark signs

·Agitation or restlessness
·Fast heart rate (tachycardia)
·Dilated pupils (mydriasis)
·Muscle twitching or jerking (myoclonus)
·Rigid or stiff muscles (especially in the legs)
·Sweating more than usual (diaphoresis)
·Confusion or trouble thinking clearly
·High fever (hyperthermia)

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Red flags · escalate now

·High fever above 104°F (40°C)—this means the body is overheating dangerously and can damage organs.
·Seizures (sudden shaking you can't stop)—the brain is firing out of control.
·Very stiff muscles that won't bend (severe rigidity)—this can break down muscle tissue and poison the kidneys.
·Fast, confused thinking that gets worse quickly—sign the brain is overwhelmed.
·Low blood pressure or trouble staying awake—means the body is starting to shut down.

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Workup

·Creatine kinase (CK)
·Basic metabolic panel (sodium, potassium, creatinine, bicarbonate)
·Complete blood count (CBC) with platelets
·Liver enzymes (AST, ALT)
·Urinalysis and urine myoglobin
·Electrocardiogram (ECG)
·CT head (non-contrast) or lumbar puncture if diagnosis is uncertain

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Treatment

·Stop all serotonin-raising medicines immediately (SSRIs, SNRIs, MAOIs, tramadol, linezolid, methylene blue, MDMA, St. John's wort)
·Cool the body aggressively if temperature ≥39°C (102.2°F): ice packs to the groin and armpits, cold IV saline, and cooling blankets
·Give lorazepam 1–2 mg IV (or diazepam 5–10 mg IV) and repeat every 10–15 minutes until the person is calm and muscles relax
·Give cyproheptadine 12 mg by mouth as the first dose, then 2 mg every 2 hours (maximum 32 mg in 24 hours) if symptoms persist
·Give IV fluids (normal saline) rapidly—start with 1–2 liters over the first hour, then continue at 200–300 mL/hour—to flush myoglobin out of the kidneys
·Do NOT give antipsychotics (haloperidol, risperidone, olanzapine) because they block dopamine and can worsen rigidity and fever
·Move to the ICU if fever stays ≥39°C after 1 hour of cooling, rigidity does not improve with benzodiazepines, heart rhythm becomes irregular, or confusion deepens

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NCLEX trap

·NEVER give antipsychotics in serotonin syndrome. Antipsychotics block dopamine (a brain messenger that helps muscles move smoothly), which makes the dangerous fever worse and cranks up muscle stiffness. Instead, give lorazepam or diazepam (medicines that help calm the brain and relax tight muscles) to ease agitation safely.
·Serotonin syndrome has rhythmic muscle jerking (clonus) (when you tap the knee, the foot bounces up and down several times on its own) and very brisk reflexes. NMS does NOT have rhythmic muscle jerking and reflexes are slow or missing. Serotonin syndrome starts within hours to 1 day after starting or increasing a serotonin drug. NMS starts after days to weeks of antipsychotic use. Check the drug timeline and test the reflexes — those two clues tell you which one it is.
·STOP all serotonin-raising drugs immediately. Serotonin syndrome happens because too much serotonin (a brain messenger that steadies mood) is flooding the brain. No treatment will work if you keep pouring in more poison. The drug must leave the body for the person to recover.
·Serotonin syndrome is a clinical diagnosis — you diagnose it by looking at the patient, not by waiting for lab results. High fever, confusion, rhythmic muscle jerking (clonus), and brisk reflexes after starting a serotonin drug IS the diagnosis. Start cooling the body and give lorazepam NOW. Every minute of delay raises the risk of organ failure and death.
·Dantrolene does NOT work for serotonin syndrome. Dantrolene stops muscles from squeezing by blocking calcium inside muscle cells, but it does nothing to block the serotonin flooding the brain. Instead, use cyproheptadine (a medicine that blocks serotonin receptors and shuts down the serotonin signal). Block the poison at its source.
·Serotonin syndrome is a body crisis that you must fix fast, but the person also has depression or anxiety that led them to start the medicine. If you send them home without therapy access, housing support, or a safer medication plan, they will crash again — either from untreated mental illness or from trying the same drug combo. Stabilize BOTH the biology AND the life supports before discharge, or the cycle repeats.

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