Which statement correctly describes the onset of NMS compared with serotonin syndrome?

• A. NMS has a slower onset; serotonin syndrome has a faster onset
• B. NMS has a faster onset; serotonin syndrome has a slower onset
• C. Both have rapid onset
• D. Both have slow onset

Answer: (A)

Onset timing is the focus. Neuroleptic malignant syndrome usually begins gradually after starting or increasing a dopamine-blocking antipsychotic, with signs evolving over 24 to 72 hours or longer. Serotonin syndrome tends to appear rapidly after adding or raising a serotonergic drug or after a drug interaction, often within hours. Because of this difference, describing NMS as having a slower onset and serotonin syndrome as having a faster onset fits the typical clinical pattern. The other patterns—both rapid or both slow—don’t reflect how these two conditions commonly present, though individual cases can vary.