What is the best medication for a 17-year-old with cannabis-induced psychosis?

Treatment of Cannabis-Induced Psychosis in a 17-Year-Old

Start with low-dose risperidone 1-2 mg/day or olanzapine 7.5-10 mg/day as first-line treatment, combined with immediate cannabis cessation and psychosocial interventions. 1, 2

Immediate Management Priorities

First, ensure this is truly psychosis and not delirium or another medical emergency:

• Confirm the patient maintains intact awareness and consciousness—if consciousness fluctuates or the patient is disoriented, this suggests delirium requiring different urgent evaluation 3
• Rule out other substance withdrawal (particularly alcohol or benzodiazepines) that could cause life-threatening complications 3
• Consider neuroimaging if there are focal neurological signs, head trauma history, or atypical features to exclude structural brain lesions 3

Immediate cannabis cessation is essential:

• Cannabis use is the most modifiable risk factor for psychosis onset and outcome 4
• Continued cannabis use during psychotic symptoms can lead to persistent psychosis 5

First-Line Medication Selection

Atypical antipsychotics are strongly preferred over typical antipsychotics due to better tolerability and fewer extrapyramidal side effects, which is critical for future medication adherence in adolescents 1

Start with one of these two options:

• Risperidone 1-2 mg/day (preferred first-line) 1, 2
• Olanzapine 7.5-10 mg/day (alternative first-line) 1, 2

Critical dosing principles for adolescents:

• Adolescents are more sensitive to both therapeutic effects and side effects than adults 2
• Use low initial doses with careful titration to minimize side effects 1
• Maximum doses should not exceed risperidone 4 mg/day or olanzapine 20 mg/day 1, 2
• Avoid large initial doses—they increase side effects without hastening recovery 3

Treatment Timeline and Monitoring

Allow adequate time for medication trial:

• Antipsychotic effects typically become apparent after 1-2 weeks 3
• Continue treatment for 4-6 weeks at therapeutic dose before determining efficacy 2, 3
• If dose increases are needed, space them at 14-21 day intervals 1

If symptoms persist after 4-6 weeks at therapeutic dose:

• Switch to a second antipsychotic with different pharmacodynamic profile 2, 3
• Options include quetiapine 100-300 mg/day or aripiprazole 15-30 mg/day 2

Essential Monitoring Requirements

Baseline and ongoing metabolic monitoring is mandatory:

• BMI, waist circumference, blood pressure 2
• HbA1c or fasting glucose, lipid panel 2
• Prolactin level, liver function tests 2
• Full blood count, electrocardiogram 2

Monitor for common side effects:

• Extrapyramidal symptoms (must be avoided to encourage future adherence) 1
• Weight gain and metabolic changes 6
• Sedation and sexual dysfunction 6

Consider metformin prophylactically if starting olanzapine to prevent metabolic complications 2

Mandatory Psychosocial Interventions

Medication alone is insufficient—psychosocial treatments are core elements:

• Provide supportive psychotherapy with active problem-solving orientation 6
• Include family in treatment plan with ongoing support and psychoeducation 6, 3
• Address cannabis use specifically with assessment and treatment strategies 7, 8
• Monitor for depression, suicide risk, and social anxiety 6
• Maintain continuity of care with same clinicians for at least 18 months 6, 3

Duration of Treatment

After symptom resolution:

• Continue maintenance treatment for 1-2 years after initial episode 2
• Once sustained remission achieved, attempt slow reduction to determine minimal effective dose 6
• Long-term medication is advisable if frequent relapses occur 6

Critical Pitfalls to Avoid

Do not:

• Use excessive doses in first-episode psychosis—this increases side effects without improving efficacy 1
• Switch medications before completing adequate 4-6 week trial 1, 2
• Neglect psychosocial interventions—they are essential, not optional 1
• Overlook family involvement in treatment 1
• Fail to address ongoing cannabis use, which can perpetuate psychosis 5
• Delay treatment if patient continues using cannabis during psychotic symptoms 5

Special Considerations for Cannabis-Induced Psychosis

The relationship between cannabis and psychosis in this patient is likely causal:

• High-dose THC is associated with psychosis, and THC concentrations have doubled from 9% in 2008 to 17% in 2017 6
• Cannabis use in adolescence causes neuropsychological decline and elevated risk for psychotic disorders in adulthood 6
• Adolescent brain development is particularly vulnerable to cannabis effects, including alterations in prefrontal cortex connectivity and heightened risk for transition to schizophrenia 6
• Cannabis-induced psychosis can become persistent if cannabis use continues during symptoms 5