Botulinum toxin complications and red flags

Reference material only. This article is general reference information, not clinical, medical or legal advice. It does not replace your clinic's own written emergency protocols, your clinical judgement, up-to-date professional guidance, or the emergency services. In an emergency, call 999 without delay. Every clinic remains responsible for its own emergency preparedness, training, equipment and drugs, and for acting within each practitioner's scope of competence and insurance.

Most botulinum toxin side effects are mild, temporary and self-limiting as the effect wears off over weeks. A few need review, and a very small number are red flags for toxin spread that require urgent medical attention.

Common, self-limiting effects

Injection-site bruising, redness or tenderness, and short-lived headache.
Minor asymmetry or an unintended brow or lid position as the effect settles.

Effects needing review

Ptosis (drooping upper eyelid) from toxin diffusing to the levator muscle. It is temporary but distressing; some prescribers use eye-drop treatments, so review and reassure.
Brow ptosis or a "heavy" brow, or an unexpected smile or lip asymmetry after lower-face treatment.
Diplopia (double vision) or dry, irritated eyes, which warrant assessment.

Red flags: possible toxin spread

Systemic spread of botulinum toxin is rare but serious. Seek urgent medical attention and call 999 if a patient develops, in the hours to days after treatment:

Dysphagia (difficulty swallowing) or difficulty breathing.
Slurred speech, a weak or hoarse voice, or generalised muscle weakness.
Trouble holding up the head, or drooping affecting swallowing or breathing.

These symptoms can indicate a medical emergency and are not something to "wait and see".

Managing and preventing

Reassure patients that most effects resolve as the toxin wears off, and document the concern and your advice. Accurate dosing, correct dilution, sound injection technique and appropriate patient selection reduce complications. Give clear aftercare, including which symptoms mean seeking urgent help, and offer a review appointment for anything troubling the patient.