What is the difference between an SSRI and an SNRI?
Last updated September 3, 2026.
SSRIs act on serotonin alone; SNRIs add norepinephrine - a chemical tied to energy, alertness, and pain. Per NIMH, that second action explains the prescribing patterns: SNRIs often get chosen when depression travels with chronic pain, nerve pain, or heavy fatigue, while SSRIs are the usual first start. Shared ground: both treat depression and anxiety, take 4 to 8 weeks to work, cause mild early side effects that fade, and need tapering rather than sudden stopping. The choice is individual chemistry, not better versus worse.
What to do
- Give the first one its weeks. Four to eight weeks before judging effect.
- Report side effects before quitting. Most fade; dose and switch options exist.
- Mention pain and fatigue explicitly. They are part of the SSRI-versus-SNRI logic.
- Never stop suddenly. Both classes need a taper. In crisis: 988 in the US, or your local crisis line.
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