Definition & epidemiology

HPPD is a substance‑induced perceptual disorder characterised by re‑experiencing visual phenomena (hallucinations, trails, afterimages) after cessation of hallucinogen use. Prevalence is low but may be under‑reported; onset can be weeks to months after exposure.

Types/subtypes

• Type 1 (Flashbacks): brief, spontaneous recurrences of perceptual phenomena similar to the acute intoxication; usually transient and episodic.
• Type 2 (Persistent HPPD): continuous or frequent visual disturbances causing significant distress or functional impairment (visual snow, trailing, haloes, micropsia/macropsia).

Common symptoms

• Visual snow (static or grainy vision), palinopsia (afterimages), trailing, halos around lights, persistent floaters, geometric visual patterns and intensified afterimages.
• Associated features: anxiety, depersonalisation, derealisation, insomnia and concentration difficulties.

Assessment & differential diagnosis

1. History: document substance(s) used, dose, frequency, timing of symptoms relative to last use and any prior visual/auditory symptoms.
2. Rule out medical/neurological causes: migraine aura, epilepsy (occipital), retinal disease, optic neuritis, medication side effects and visual pathway lesions — consider neuro‑ophthalmology/neuroimaging where indicated.
3. Assess psychiatric comorbidity: anxiety disorders, PTSD and depersonalisation frequently co‑occur and worsen distress.
4. Use visual symptom questionnaires or structured assessments to track severity and functional impact.

Investigations

• Baseline: visual acuity, fundoscopy, and basic blood tests to rule out metabolic causes.
• Consider EEG if focal seizures suspected, and MRI brain if atypical features (focal deficits, progressive symptoms) or to exclude structural causes.
• Referral to ophthalmology or neurology if examination abnormal or symptoms persistent despite initial management.

Management principles

• Reassurance and psychoeducation: explain the benign (non‑progressive) nature in most cases, the role of substance re‑exposure in worsening symptoms and set realistic recovery expectations.
• Avoid re‑exposure to hallucinogens and other agents that may exacerbate symptoms (cannabis, stimulants, alcohol in some cases).
• Address comorbid anxiety, sleep disturbance and attentional problems as these amplify distress from perceptual symptoms.
• Use a stepwise approach: first‑line non‑pharmacological interventions (CBT, coping strategies), then pharmacological options for refractory cases under specialist guidance.

Non‑pharmacological treatments

• Cognitive‑behavioural therapy focusing on symptom management, anxiety reduction and behavioural strategies to reduce functional impact.
• Visual coping strategies: contrast filters, screen adjustments, good sleep hygiene, and paced exposure to triggering visual stimuli.
• Mindfulness, grounding techniques and occupational strategies to improve concentration and reduce avoidance.

Pharmacological options (limited evidence)

• Clonazepam: some case series show symptomatic benefit — risk of dependence and sedation requires careful risk–benefit discussion.
• Lamotrigine: used in some refractory HPPD cases with anecdotal benefit; monitor for rash and follow standard titration.
• SSRIs/SNRIs: may assist comorbid anxiety/depression but can occasionally worsen perceptual symptoms in some patients — start low and monitor.
• Antipsychotics: generally avoid unless clear comorbid psychosis — some antipsychotics may worsen visual symptoms.
• All pharmacological interventions should be guided by psychiatry/neurology and tailored to individual risk profiles.

When to refer & prognosis

• Refer to psychiatry or neuro‑ophthalmology if symptoms are severe, progressive, or refractory to initial measures.
• Prognosis: many patients experience gradual improvement over months to years; a subset have persistent symptoms requiring long‑term management.

Key takeaways

• HPPD presents with persistent visual disturbances after hallucinogen use — assess thoroughly to exclude other neurological/ophthalmic causes.
• Start with psychoeducation, avoidance of re‑exposure and CBT for coping; reserve medications (clonazepam, lamotrigine) for selected refractory cases under specialist oversight.
• Provide multidisciplinary follow‑up (psychiatry, neurology, ophthalmology) for severe or persistent cases and set realistic recovery expectations.