Serotonin toxicity is diagnosed by seven signs, and the rules were built from 2,222 overdoses
The Hunter criteria: clonus, agitation, sweating, tremor and hyperreflexia predict serotonin toxicity; rigidity and fever above 38 degrees mark the life-threatening form. Sensitivity 84 percent against 75 for the old rules, specificity 97.
Suggestive but preliminary. Not settled. how we score evidence
Caveat on this rating: Derived from overdose admissions at one Australian toxicology service; performance in therapeutic-dose interactions, which are usually milder, was not the setting studied.
Half the labels in this wave warn about serotonin syndrome. This is the paper that defined how a clinician recognises it.
Significant findings
Dunkley and colleagues (QJM, 2003) studied "all patients admitted to the Hunter Area Toxicology Service (HATS) following an overdose of a serotonergic drug from January 1987 to November 2002 (n = 2222)." A learning set of 473 SSRI-alone overdoses was used to find which clinical features predicted a toxicologist's diagnosis of serotonin toxicity.
"Numerous clinical features were associated with serotonin toxicity, but only clonus (inducible, spontaneous or ocular), agitation, diaphoresis, tremor and hyperreflexia were needed for accurate prediction of serotonin toxicity as diagnosed by a clinical toxicologist. Although the learning dataset did not include patients with life-threatening serotonin toxicity, hypertonicity and maximum temperature > 38 degrees C were universal in such patients; these features were therefore added."
The result: "These new criteria were simpler, more sensitive (84% vs. 75%) and more specific (97% vs. 96%) than Sternbach's criteria."
Worth asking
The everyday value of this paper is the symptom list in plain words: muscle twitching or jerking that a doctor can trigger by flexing your ankle, restlessness, sweating, tremor, overactive reflexes, and in severe cases stiffness and fever. Nausea or a headache after starting a second serotonergic drug is not on the list. If you have been told to watch for serotonin syndrome, these seven signs are what to watch for, and they are a reason to seek care the same day.
Source
The Hunter Serotonin Toxicity Criteria: simple and accurate diagnostic decision rules for serotonin toxicity — Dunkley EJ, Isbister GK, Sibbritt D, Dawson AH, Whyte IM (2003)
Reputable peer-reviewed journal
Read the source: https://doi.org/10.1093/qjmed/hcg109
DOI: 10.1093/qjmed/hcg109
How this was scored
- Study design
- Cross-sectional study / survey
- Funding
- Funding not disclosed
- Published in
- Reputable peer-reviewed journal
- Sample size
- 2,222
- Preregistered
- not recorded
- Conflicts disclosed
- not recorded
- Independent of proponent
- not recorded
- Retracted
- No
Read the full scoring rubric, including what it can't tell you.
Published September 21, 2026.
Questions
How strong is the evidence behind this?
veisund rates this source "early signal". Suggestive but preliminary. Not settled. It scores 45 out of 100 on our published rubric. One caveat travels with that badge: Derived from overdose admissions at one Australian toxicology service; performance in therapeutic-dose interactions, which are usually milder, was not the setting studied. The score is calculated from recorded facts about the source — study design, funding, publication venue, sample size, preregistration — not typed in by an editor.
What is the source for this?
The Hunter Serotonin Toxicity Criteria: simple and accurate diagnostic decision rules for serotonin toxicity — Dunkley EJ, Isbister GK, Sibbritt D, Dawson AH, Whyte IM (2003). Published in: Reputable peer-reviewed journal. DOI: 10.1093/qjmed/hcg109. The full source is linked on this page so you can read it yourself.
Who paid for this research, and does that matter?
Study design: Cross-sectional study / survey. Funding: Funding not disclosed. Independence from the proponent is not recorded. Industry sponsorship is one of the most reliably measured biases in medicine, which is why funding carries real weight in the score rather than sitting in a footnote.
Is this medical advice?
This is information to bring to your prescriber, not medical advice and not a reason to change anything on your own. Nothing here is an instruction to stop or reduce a medication. If you are in crisis, call or text 988.
This is information to bring to your prescriber, not medical advice and not a reason to change anything on your own. Nothing here is an instruction to stop or reduce a medication. If you are in crisis, call or text 988.