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BASICS

Medical marijuana or medical cannabis refers to the use of pharmacologic agents derived from the flowering plant genus Cannabis to treat disease or alleviate symptoms.

DESCRIPTION
Marijuana plants contain >100 phytocannabinoids, molecules with affinity for mammalian cannabinoid receptors:
- CB1: highly expressed in the central nervous system
- CB2: expressed in the periphery, including the immune system

Routes of administration include inhalation (smoking, vaporized), oral ingestion (edibles), and topical (oral mucosa or skin).

EPIDEMIOLOGY

  • In the U.S., 36 states and 4 territories allow medical cannabis, though illegal federally.
  • 49 countries worldwide have legalized medical cannabis.
  • Estimated prevalence in U.S. primary care: 2%; recreational use: 15%.

TREATMENT

Qualified conditions vary by state; most common include:
- Chronic pain
- Cancer-related weight loss, nausea, vomiting
- Epilepsy

Evidence (1)[A]:
- Chronic pain: low-strength evidence for neuropathic pain relief; 40% greater pain improvement vs. placebo.
- Chemotherapy-induced nausea/vomiting: oral THC (dronabinol, nabiximols) effective.
- MS muscle spasticity: oral cannabinoids effective for patient-reported spasticity symptoms.
- Anorexia/cachexia (HIV/AIDS, cancer): low-quality evidence of weight gain with dronabinol.
- PTSD: limited, conflicting evidence.
- Seizures: insufficient evidence except FDA-approved cannabidiol (Epidiolex) for Lennox-Gastaut and Dravet syndromes.

GENERAL MEASURES

  • States may require patient registries, ID cards, and provider education.
  • Certifying providers do not prescribe cannabis, only certify qualifying conditions.

MEDICATION

FDA-approved products:
- Dronabinol (Marinol): THC, 2.5 mg BID, max 20 mg/day (chemotherapy-induced nausea, AIDS anorexia)
- Nabilone (Cesamet): THC analog, 1 mg BID, max 6 mg/day
- Epidiolex: CBD oral solution for seizures, 2.5 mg/kg BID, max 20 mg/kg/day
- Nabiximols (Sativex): THC/CBD 1:1 buccal spray for MS spasticity, cancer/neuropathic pain

ONGOING CARE

Pediatric Considerations:
- Increased poison center calls with legalization.
- Exposure risks: respiratory depression, tachycardia, coma.
- Adolescents vulnerable to long-term brain changes (lower IQ, school dropout).

Pregnancy/Lactation:
- No approved indications; marijuana use discouraged.
- Concern for impaired fetal neurodevelopment.

COMPLICATIONS

Short-term:
- Intoxication (tachycardia, orthostatic hypotension, dry mouth, poor coordination, euphoria).
- Withdrawal (irritability, depression, insomnia).
- Increased motor vehicle accident risk (RR=2).

Long-term:
- Respiratory symptoms and bronchitis with smoking.
- Possible increased risk of acute MI and stroke.
- Limited/no evidence linking cannabis to most cancers.
- Psychological effects: increased anxiety, psychosis, depression, schizophrenia risk in early users.
- Addiction risk ~9% overall, higher in adolescents/daily users.

Other:
- Cannabis-induced hyperemesis syndrome.
- Associated hepatotoxicity.

REFERENCES

  1. Ebbert JO, Scharf EL, Hurt RT. Medical cannabis. Mayo Clin Proc. 2018;93(12):1842-1847.
  2. Whiting PF, Wolff RF, Deshpande S, et al. Cannabinoids for medical use: systematic review and meta-analysis. JAMA. 2015;313(24):2456-2473.
  3. National Academies of Sciences, Engineering, and Medicine. The Health Effects of Cannabis and Cannabinoids. 2017.
  4. National Conference of State Legislatures. State medical marijuana laws.
  5. Sazeger P. Cannabis essentials: tools for clinical practice. Am Fam Physician. 2021;104(6):598-608.
  6. Gloss D, Vickrey B. Cannabinoids for epilepsy. Cochrane Database Syst Rev. 2014;2014(3):CD009270.
  7. ACOG Committee Opinion No. 637: marijuana use during pregnancy and lactation. Obstet Gynecol. 2015;126(1):234-238.

Clinical Pearls

  • Current evidence shows modest benefit in limited conditions.
  • Oral cannabinoids effective for chemotherapy-induced nausea/vomiting.
  • Medical cannabis may be useful adjunct for chronic pain in selected patients.
  • Counsel users about accidental pediatric ingestion risks.