Clozapine-specific adverse effects

Constipation, ileus, myocarditis, heavy sedation, sialorrhoea, seizure, fever, neutropenia

EmergentReview due

At a glance

High risk: Yes
Onset: Variable
Course: Dose-linked
Treatable: Yes

Safety snapshot

Severe constipation/abdominal pain, tachycardia with chest pain/dyspnoea, CRP/troponin rise, neutropenic sepsis, seizure, aspiration.

Watch forSevere constipation/abdominal paintachycardia with chest pain/dyspnoeaCRP/troponin riseneutropenic sepsis

Presentation hinge

Temporal association with antipsychotic initiation, dose change, or depot timing.

Separates the Medication Side Effects / Iatrogenic Toxicity / QT Risk group. It is not specific to Clozapine-specific adverse effects.

Do now

1Establish whether any dose has been missed and for how long, because a sustained break means retitrating from the start rather than resuming the previous dose. The exact cut-off sits in the local clozapine protocol
2Take temperature and pulse, and send FBC with differential, CRP, troponin and an ECG in the first weeks of treatment, because myocarditis presents as a flu-like illness
3Ask about constipation at every review and treat it actively, because clozapine-induced gastrointestinal hypomotility is a recognised cause of death and is easier to miss than the haematological monitoring already in place
4Check for smoking cessation, intercurrent infection or an interacting medicine before attributing a rise in effect to the dose alone
5Discuss with the clozapine coordinator and the treating consultant before any change, and follow the local monitoring protocol

Locally authored, reviewed by PsychSift on 27 September 2026

Clinical review

Rows marked “Whole group”: Applies to the Medication Side Effects / Iatrogenic Toxicity / QT Risk group — not specific to Clozapine-specific adverse effects

Why it fits

Constipation, ileus, myocarditis, heavy sedation, sialorrhoea, seizure, fever, neutropenia

Key features

Must-not-miss

Severe constipation/abdominal pain, tachycardia with chest pain/dyspnoea, CRP/troponin rise, neutropenic sepsis, seizure, aspiration.

High-risk causes6 causes

Severe constipation/abdominal pain
tachycardia with chest pain/dyspnoea
CRP/troponin rise
neutropenic sepsis
seizure
aspiration

Bedside question

Applies to the Medication Side Effects / Iatrogenic Toxicity / QT Risk group.

Temporal association with antipsychotic initiation, dose change, or depot timing.

Helpful clues

Immediate action

Applies to the Medication Side Effects / Iatrogenic Toxicity / QT Risk group.

Constipation with clozapine is a red flag, not a nuisance side effect Clozapine constipation and myocarditis are high-risk problems Escalate early, review bowels deliberately, maintain active surveillance during early titration Early activation is a common misread Clinical toxicity can occur even when history suggests a "usual dose" Check ammonia if unexplained confusion develops on valproate

Priority steps6 steps

1Constipation with clozapine is a red flag, not a nuisance side effect
2Clozapine constipation and myocarditis are high-risk problems
3Escalate early, review bowels deliberately, maintain active surveillance during early titration
4Early activation is a common misread
5Clinical toxicity can occur even when history suggests a "usual dose"
6Check ammonia if unexplained confusion develops on valproate

Investigations

Applies to the Medication Side Effects / Iatrogenic Toxicity / QT Risk group.

ECG / QT assessment, Urea, electrolytes, creatinine, Inflammatory markers (CRP/ESR), Creatine kinase

Core tests4

ECG / QT assessment
Urea, electrolytes, creatinine
Inflammatory markers (CRP/ESR)
Creatine kinase

Mimics / overlap

Applies to the Medication Side Effects / Iatrogenic Toxicity / QT Risk group.

None listed

Consider

Do now

1Establish whether any dose has been missed and for how long, because a sustained break means retitrating from the start rather than resuming the previous dose. The exact cut-off sits in the local clozapine protocol
2Take temperature and pulse, and send FBC with differential, CRP, troponin and an ECG in the first weeks of treatment, because myocarditis presents as a flu-like illness
3Ask about constipation at every review and treat it actively, because clozapine-induced gastrointestinal hypomotility is a recognised cause of death and is easier to miss than the haematological monitoring already in place
4Check for smoking cessation, intercurrent infection or an interacting medicine before attributing a rise in effect to the dose alone
5Discuss with the clozapine coordinator and the treating consultant before any change, and follow the local monitoring protocol

Locally authored, reviewed by PsychSift on 27 September 2026

First-line tests

Applies to the Medication Side Effects / Iatrogenic Toxicity / QT Risk group — not specific to Clozapine-specific adverse effects

ECG / QT assessment
Urea, electrolytes, creatinine
Inflammatory markers (CRP/ESR)
Creatine kinase

Watch for

Severe constipation/abdominal pain
tachycardia with chest pain/dyspnoea
CRP/troponin rise
neutropenic sepsis

Also consider

Source and review

Review due· Unverified

v10 · exported 2026-07-11

Clinical reference — not validated decision support. Review before use.