Cannabis Induced Anxiety

Cannabis induced anxiety is anxiety or panic that occurs during cannabis intoxication, or during withdrawal after regular use, or as an ongoing anxiety disorder that is maintained or worsened by cannabis. Delta-9-tetrahydrocannabinol (THC), a partial agonist at CB1 receptors, causes dose dependent anxiety, whereas cannabidiol has the opposite effect.

• Acute effects appear within minutes when smoked or vaporised (peak at 30 minutes, lasting 2 to 4 hours) and within 30 to 120 minutes when eaten (peak at 2 to 4 hours, lasting 6 to 12 hours or longer), so delayed onset with edibles often leads to taking too much.
• Risk factors: high potency products (THC content over 15 to 20 percent), naive users, large doses, adolescence, pre-existing anxiety or psychosis risk, family history of psychosis, use with alcohol, stimulants or caffeine, and synthetic cannabinoids (spice, K2), which cause severe agitation, psychosis, seizures and cardiac complications.
• Chronic use is associated with persistent anxiety, depression, sleep disturbance and cannabis use disorder; about 1 in 10 users (1 in 6 starting in adolescence) develop dependence.
• Cannabis withdrawal produces irritability, anxiety, insomnia, reduced appetite, restlessness and low mood within 24 to 72 hours of stopping, peaking at days 2 to 6 and lasting 1 to 3 weeks.

• Intoxication: sudden fear, panic, feeling of losing control or dying, depersonalisation and derealisation, paranoid thoughts, time distortion, restlessness, with tachycardia, conjunctival injection, dry mouth, increased appetite, impaired coordination and postural hypotension.
• Severe: transient psychotic symptoms (hallucinations, delusions), confusion, syncope, chest pain, arrhythmia (atrial fibrillation, ventricular arrhythmia), myocardial infarction (rare), accidental ingestion in children (lethargy, ataxia, hypotonia, respiratory depression).
• Withdrawal: irritability, anger, nervousness, insomnia with vivid dreams, abdominal pain, tremor, sweating, headache, and craving.
• Chronic: persistent worry, social anxiety, panic attacks, amotivation, and a pattern of using to relieve anxiety, which worsens it over time.
• Ask about type and potency of product, route, quantity and frequency, alcohol and other drugs, mental health history, psychosis, and driving.

• Clinical, based on the temporal relationship with cannabis use and exclusion of other causes.
• Examination: vital signs, pupils, cardiac rhythm, orientation, mental state, capillary glucose.
• Investigations (if severe, atypical or first episode): ECG, glucose, electrolytes, urine drug screen (detects metabolites of THC for days to weeks, so it does not prove intoxication), troponin if chest pain, pregnancy test.
• Screen for cannabis use disorder (CUDIT-R, 8 or more suggests hazardous use) and for depression, anxiety (GAD-7), and psychotic symptoms.
• Differentials: primary anxiety or panic disorder, psychotic disorder, intoxication with other stimulants or synthetic cannabinoids, hyperthyroidism, hypoglycaemia, arrhythmia, alcohol or benzodiazepine withdrawal, phaeochromocytoma, delirium.

Acute anxiety or panic with intoxication

• Reassure in a calm, quiet, low stimulation room with a trusted person; explain that effects are temporary and will pass; encourage slow breathing; offer fluids and food; do not leave the patient alone; monitor for 2 to 4 hours (longer after edibles).
• Medication only if severe agitation, distressing panic or tachycardia persists: lorazepam 1 to 2 mg orally (or diazepam 5 to 10 mg orally); repeat once after 1 hour if needed. Avoid in respiratory depression and mixed sedative intoxication.
• Propranolol 10 to 20 mg orally for marked palpitations in a patient with no asthma or heart block.
• Antipsychotic for persistent psychosis or severe agitation: olanzapine 5 to 10 mg orally or haloperidol 2.5 to 5 mg orally or intramuscularly, after a benzodiazepine and ECG.
• Treat chest pain and arrhythmia with emergency assessment. Children with accidental ingestion: observe, intravenous fluids, airway support, and activated charcoal only in the first hour for substantial ingestions.
• Do not drive for at least 6 hours after smoking, and 8 to 12 hours after eating cannabis.

Withdrawal

• Supportive care: psychoeducation, regular sleep routine, exercise, hydration, avoid caffeine and alcohol; short term symptomatic treatment: paracetamol or ibuprofen for headache, hydroxyzine 25 mg at night for insomnia, or zolpidem 5 mg for up to 1 week.
• No licensed medicine; nabiximols or gabapentin 300 mg three times daily increasing to 1200 mg daily have limited evidence in specialist programmes.

Longer term treatment

• Motivational interviewing and brief intervention in every patient; cognitive behavioural therapy and contingency management for cannabis use disorder; a family based programme for young people.
• Treat the underlying anxiety disorder: cognitive behavioural therapy and sertraline 25 to 50 mg daily increasing to 100 to 200 mg, or escitalopram 5 to 10 mg increasing to 20 mg, with a planned reduction in cannabis use. Avoid long term benzodiazepines.
• Screen for psychosis; refer early to early intervention services if psychotic symptoms persist more than 24 hours after use or recur.
• Smoking cessation (tobacco mixed in joints), reduce high potency products, and advise abstinence or reduced use.

Follow up

• Review at 1 to 2 weeks and then monthly; re-screen anxiety and cannabis use; refer to addiction services for cannabis use disorder.

Special groups

• Adolescents: higher risk of persistent psychosis and anxiety; advise abstinence and involve parents.
• Pregnancy and breastfeeding: advise stopping; THC passes into milk and is linked to low birth weight and neurodevelopmental effects.
• Heart disease: cannabis can trigger arrhythmia and infarction; advise against use.