Compare SSRI medication in these side effects: somnolence Fatigue or reduced

Guideline-aligned answer with reasoning, red flags and references. Clinically reviewed by Dr Kola Tytler MBBS CertHE MBA MSt MRCGP.

Posted: 5 August 2026Updated: 5 August 2026 Guideline-Aligned (High Confidence) Clinically Reviewed

Evidence-limited comparison: The supplied UK sources provide adverse-effect frequencies only for fluoxetine and sertraline; they do not provide a common numerical severity scale, direct head-to-head comparisons, or sufficient data to rank citalopram, escitalopram, paroxetine, and fluvoxamine. ,,,

Interpretation of scores: Scores below are pragmatic comparative estimates of likelihood/burden from the supplied SmPC frequency categories, where 1 is least and 10 is greatest; they are not validated clinical severity scores. ,,,

  • Fluoxetine: Somnolence/fatigue or reduced energy 6/10; sexual dysfunction 7/10; weight gain 1/10; anxiety/activation 6/10. Fluoxetine lists fatigue among its most commonly reported adverse reactions, while somnolence, lethargy, reduced libido, erectile dysfunction, ejaculation disorder, sexual dysfunction, anxiety, nervousness, restlessness and tension are reported adverse reactions. Weight decrease, rather than weight gain, is listed as an adverse reaction.
  • Sertraline: Somnolence/fatigue or reduced energy 5/10; sexual dysfunction 8/10; weight gain 3/10; anxiety/activation 6/10. Sertraline lists somnolence as a very common adverse reaction, and anxiety, agitation, reduced libido and nervousness as common adverse reactions. ,, In social anxiety disorder studies, ejaculation failure occurred in 14% of men receiving sertraline versus 0% receiving placebo, and sexual adverse effects are described as dose-dependent and often transient. ,, Increased appetite is reported, but the supplied sertraline excerpts do not establish weight gain as an adverse reaction. ,,
  • Citalopram, escitalopram, paroxetine and fluvoxamine: No 1–10 rankings can be derived responsibly from the supplied excerpts because they contain no adverse-effect frequency or comparative burden data for these medicines in the requested domains. ,,,

Relative ranking among medicines with usable supplied data: For somnolence/fatigue, fluoxetine is estimated slightly higher than sertraline because fluoxetine specifically identifies fatigue among its most commonly reported reactions, whereas the supplied sertraline data identify somnolence but not fatigue. ,,, For sexual dysfunction, sertraline is estimated slightly higher because the supplied data quantify a 14% ejaculation-failure rate in men with social anxiety disorder, while fluoxetine lists sexual adverse reactions without a corresponding numerical incidence. ,,, For weight gain, neither fluoxetine nor sertraline has supplied evidence of established weight gain; fluoxetine instead lists weight decrease, and sertraline lists increased appetite. ,,, For anxiety/activation, both are scored similarly because fluoxetine lists anxiety, nervousness, restlessness and tension, while sertraline lists anxiety, agitation and nervousness. ,,,

Clinical application: The occurrence and burden of adverse effects are individual and may improve with continued treatment; sertraline sexual adverse effects are dose-dependent, and NICE advises low-dose initiation with slow titration to reduce initiation side effects. ,,,, If early adverse effects are unacceptable, NICE advises considering stopping or switching antidepressant after discussion with the patient.

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