Who Should Not Use Cannabis
Absolute Contraindications
- Personal history of psychotic disorders (schizophrenia, schizoaffective disorder)
- Pregnancy or breastfeeding
- Unstable cardiovascular disease
- Under 25 with first-degree family history of psychosis
- Active non-cannabis substance use disorder
Use with Caution
- History of anxiety/panic (THC can exacerbate; consider CBD-dominant products)
- History of depression (complex relationship — monitor closely)
- Age under 25 (neurodevelopmental concerns)
- Respiratory disease (avoid combustion; consider edibles/tinctures)
- Hepatic impairment (altered metabolism of cannabinoids)
Key Drug Interactions
Cannabis (particularly CBD) inhibits CYP3A4, CYP2C19, and CYP2C9 enzymes. THC is a substrate of CYP2C9 and CYP3A4.
| Drug Class | Interaction | Clinical Significance | Recommendation |
|---|---|---|---|
| Warfarin | CBD/THC inhibit CYP2C9 → increased warfarin levels | High — bleeding risk | Monitor INR closely. May need dose reduction. |
| Clobazam | CBD inhibits CYP2C19 → increased clobazam/norclobazam | High — sedation, toxicity | Relevant for epilepsy patients on Epidiolex. Dose adjustment needed. |
| Benzodiazepines | Additive CNS depression + metabolic inhibition | Moderate-High | Increased sedation risk. Monitor and consider dose reduction. |
| Opioids | Additive CNS/respiratory depression | Moderate-High | Monitor respiratory function. May allow opioid dose reduction. |
| SSRIs / SNRIs | CYP2C19 inhibition → increased SSRI levels | Moderate | Monitor for serotonergic side effects. May need SSRI dose adjustment. |
| Immunosuppressants (tacrolimus, cyclosporine) | CYP3A4 inhibition → increased levels | Moderate-High | Monitor drug levels closely. Transplant patients at particular risk. |
| Statins | CYP3A4 inhibition → increased statin levels | Low-Moderate | Monitor for myopathy symptoms. Consider lower statin dose. |
Signs of Cannabis Use Disorder
Approximately 10% of all cannabis users and ~30% of regular users develop CUD (DSM-5). Watch for these patterns:
- Using more or longer than intended
- Unsuccessful attempts to cut down
- Significant time spent obtaining, using, or recovering
- Craving or strong urges to use
- Use interfering with work, school, or home responsibilities
- Continued use despite social or relationship problems
- Giving up important activities because of use
- Use in physically hazardous situations
- Continued use despite physical or psychological problems
- Tolerance (needing more for same effect)
- Withdrawal symptoms when stopping
Severity: Mild (2-3 criteria), Moderate (4-5), Severe (6+). For screening tools and clinical handouts, see our companion site's Screening Tools.
When to Refer
Consider referral to addiction medicine or specialized treatment when:
- CUD criteria are met and patient is unable to reduce use despite wanting to
- Co-occurring psychosis or psychotic symptoms emerging with use
- Suicidal ideation — immediate safety planning required
- Polysubstance use — concurrent alcohol, opioid, or stimulant use disorder
- Cannabinoid hyperemesis syndrome — recurrent severe vomiting with hot-water bathing compulsion
- Patient request — patient expressing desire for more structured help
Useful Clinical Resources
- SAMHSA Treatment Locator — Find local treatment programs
- CannabisDependence.org — For Therapists — Screening tools, withdrawal handouts, relapse prevention worksheets
- Flockhart CYP450 Table — Drug interaction reference
Cannabis and cannabinoids interact with multiple cytochrome P450 enzymes, particularly CYP3A4 and CYP2C19. Clinicians should review potential interactions with any patient using cannabis products, especially those on narrow therapeutic index drugs.
Nasrin et al., Drug Metabolism Reviews, 2021
For support with quitting or cutting back on cannabis, visit our companion site CannabisDependence.org