What psychiatric medications can cause mydriasis?

Psychiatric Medications That Cause Mydriasis

Tricyclic antidepressants, anticholinergic drugs, and certain antipsychotics are the main psychiatric medications that cause mydriasis (pupillary dilation). 1

Medications with Strong Mydriatic Effects

Tricyclic Antidepressants (TCAs)

• TCAs commonly cause mydriasis due to their anticholinergic properties 1
• Examples include:
  • Amitriptyline - FDA label specifically lists mydriasis as an anticholinergic side effect 2
  • Imipramine - Can cause mydriasis and disturbances of accommodation 3
• The mydriatic effect is often transient but can promote closure of angles in susceptible patients 1

Anticholinergic Medications

• Anticholinergic drugs used in psychiatry frequently cause mydriasis 4
• These include:
  • Antihistamines with anticholinergic properties 4
  • Tricyclic antidepressants (as mentioned above) 4
  • Sleep aids with anticholinergic properties 4
  • Atropine and related compounds 5
• The mydriatic effect occurs through blocking muscarinic receptors in the iris sphincter muscle 6

Antipsychotics

• Certain antipsychotics can cause mydriasis, particularly:
  • Low-potency typical antipsychotics 4
  • Some atypical antipsychotics 1
• The anticholinergic syndrome from antipsychotic overdose classically presents with mydriasis ("blind as a bat") 4

Clinical Significance and Risks

Risk of Angle-Closure Glaucoma

• TCAs and antipsychotics with anticholinergic properties can precipitate angle-closure glaucoma in predisposed patients 1
• When patients with narrow angles are given TCAs, they appear to experience induction of glaucomatous attacks 1
• This risk is particularly important in elderly patients or those with pre-existing narrow angles 1

Diagnostic Value

• Mydriasis is a key physical examination finding in anticholinergic toxicity syndrome 4
• The classic description of anticholinergic syndrome includes mydriasis ("blind as a bat") along with dry mucous membranes, flushed skin, hyperthermia, and altered mental status 4

Clinical Management Considerations

Monitoring and Prevention

• Patients with narrow-angle glaucoma should be carefully monitored when prescribed medications with mydriatic effects 1
• Miotic eye drops (like pilocarpine) can be used prophylactically in high-risk patients who must receive anticholinergic medications 5

Treatment of Mydriasis

• Most medication-induced mydriasis is transient and resolves with discontinuation or dose reduction 1
• In cases of anticholinergic toxicity with mydriasis, physostigmine may be considered for severe symptoms 4

Differential Diagnosis

• Mydriasis can also occur in serotonin syndrome, but is not as characteristic as in anticholinergic toxicity 4
• Other causes of mydriasis include sympathomimetic drugs, withdrawal from dopaminergic drugs, and neurological conditions 4

Remember that medication-induced mydriasis can be an early warning sign of more serious anticholinergic effects and should prompt careful evaluation, especially in patients with risk factors for angle-closure glaucoma 1.