Medical Marijuana: An Evidence-Based Overview

Medical marijuana refers to the use of Cannabis plants—or extracts thereof—for symptom relief in the context of diagnosed medical conditions. Unlike recreational use, its therapeutic intent is not intoxication but alleviation of symptoms such as pain, nausea, spasticity, or seizures—when conventional treatments have proven inadequate or intolerable (National Academies of Sciences, Engineering, and Medicine [NASEM], 2017). Importantly, “medical marijuana” is not a cure for disease; rather, it serves as a potential component of integrative symptom management.

Botanical Basis and Composition
Cannabis belongs to the family Cannabaceae and comprises three primary species: C. sativa, C. indica, and C. ruderalis. While all contain bioactive compounds, most clinical formulations derive from C. sativa or C. indica strains selectively bred for consistent cannabinoid profiles.

The plant produces over 140 phytocannabinoids, with delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) being the most extensively studied. THC is psychoactive; CBD is non-intoxicating and modulates THC’s effects (Pertwee, 2015). Additional minor cannabinoids (e.g., CBG, CBN) and terpenes contribute to the “entourage effect,” potentially enhancing therapeutic outcomes while mitigating adverse reactions (Russo, 2019).

Pharmacology of the Endocannabinoid System
The human body contains an endogenous cannabinoid system comprising:

• CB₁ receptors: Predominantly in the central and peripheral nervous systems. Activation by THC produces psychoactive effects but also analgesia, antiemesis, and appetite stimulation.
• CB₂ receptors: Primarily expressed on immune cells; modulation may reduce inflammation and neuropathic pain (Hohmann et al., 2015).

THC acts as a partial agonist at CB₁ and CB₂ receptors. CBD has low affinity for these receptors but influences multiple non-cannabinoid pathways—including serotonin 5-HT₁A, TRPV1, and glycine receptors—and inhibits endocannabinoid breakdown (e.g., by blocking FAAH), thereby exerting anticonvulsant, anti-inflammatory, and anxiolytic effects (Iffland & Grotenhermen, 2017).

Due to high lipophilicity, cannabinoids exhibit extensive tissue distribution, slow elimination half-lives (up to several days for chronic users), and placental/fetal transfer—raising concerns about developmental toxicity during pregnancy (Volkow et al., 2016).

Epidemiology of Use
Globally, an estimated 192 million people used cannabis in 2020 (~4.1% of the adult population), with ~48 million using it annually (World Health Organization [WHO], 2023). In the U.S., 52.5 million people (19.4% of those aged 12+) reported past-year use in 2022, including 14.5 million adolescents and young adults (12–25 years) (National Survey on Drug Use and Health [NSDUH], 2022). While cannabis is the most commonly used illicit substance worldwide, patterns of medical vs. recreational use differ significantly by jurisdiction.

Routes of Administration and Pharmacokinetics

* Topicals generally do not produce systemic effects or intoxication.

Inhalation offers rapid titration and predictable dosing—advantageous for acute symptoms. Oral routes provide longer duration but exhibit variable absorption and first-pass metabolism (Dlugos et al., 2019).

Evidence-Based Therapeutic Applications
The strongest clinical evidence supports medical Cannabis use for:

• Chemotherapy-Induced Nausea and Vomiting (CINV): THC-based antiemetics (dronabinol, nabilone) are FDA-approved and effective in refractory cases (Grigg et al., 2013).
• Chronic Pain: Meta-analyses confirm modest efficacy for neuropathic, inflammatory, and cancer-related pain—but risks often outweigh benefits for long-term monotherapy (NASEM, 2017; Whiting et al., 2015).
• Multiple Sclerosis (MS)-Related Spasticity: Nabiximols (Sativex®), a 1:1 THC:CBD oromucosal spray, is approved in >30 countries and reduces spasticity by ~20% over placebo in randomized trials (Chaudhary et al., 2020).
• Epilepsy: Epidiolex® (purified CBD oral solution) significantly reduces seizure frequency in Lennox-Gastaut and Dravet syndromes (Devinsky et al., 2017, 2023). FDA-approved in 2018.
• Appetite Stimulation in HIV/AIDS: Dronabinol improves weight gain and appetite in wasting syndrome (Meacham & Gourlay, 2004).

Emerging evidence suggests potential benefits for PTSD-related nightmares (Mitchell et al., 2021), inflammatory bowel disease (IBD) symptom control (Naumovski et al., 2020), and palliative care—though larger Phase III trials are needed.

Note: Evidence for tumor regression or cancer cell destruction in humans remains preclinical (in vitro/animal models); no robust clinical trial supports cannabis as an oncologic therapy (National Cancer Institute, 2023).

Legal and Regulatory Landscape

• United States: Despite federal Schedule I classification (DEA), 38 states + DC, Puerto Rico, Guam, and the U.S. Virgin Islands have legalized medical cannabis (NCSL, 2024). Patients require physician certification and state-issued registry ID cards to access dispensaries.

• FDA-Approved Cannabinoid Medicines:

  • Dronabinol (Marinol®, Syndros®): Synthetic THC for CINV and AIDS wasting.
  • Nabilone (Cesamet®): Synthetic THC analog for CINV.
  • Sativex®: THC:CBD combination for MS spasticity (not FDA-approved but used in clinical trials).
  • Epidiolex®: CBD for seizures (2018 approval).

• Global: Over 50 countries permit medical cannabis, including Germany, Canada, Israel, and the UK. Regulatory models range from prescription-only pharmaceuticals (e.g., Sativex® in the UK) to state-regulated dispensary systems (Canada, Germany) (United Nations Office on Drugs and Crime [UNODC], 2022).

Safety Profile and Adverse Effects
Short-term effects include dizziness, dry mouth, tachycardia, impaired coordination, and acute anxiety/paranoia—dose-dependent and more common with high-THC products (Bhattacharyya et al., 2016). Long-term risks include:

• Cognitive Effects: Adolescent-onset heavy use correlates with persistent declines in IQ (~5–8 points) and impaired executive function (Meier et al., 2018).
• Psychiatric Risks: Associated with increased psychosis risk in vulnerable individuals (diathesis-stress model); cannabis use disorder (CUD) affects ~9% of users, rising to 16.7% among those initiating use before age 17 ( HAS, 2023; NIDA, 2020).
• Respiratory: Smoking cannabis exposes users to carcinogens similar to tobacco smoke; vaping-linked lung injury (EVALI) was linked to vitamin E acetate in illicit THC cartridges (CDC, 2020).
• Cardiovascular: Modest short-term risk of MI and arrhythmia—particularly in those with preexisting heart disease (Bhatt et al., 2022).

Contraindications: Pregnancy (risk of low birth weight, developmental delays), adolescents (<25 years), individuals with personal/family psychosis history, and severe cardiovascular disease (FDA, 2021; American Academy of Pediatrics, 2015).

Addiction and Withdrawal
Cannabis use disorder (CUD) is diagnosed per DSM-5 criteria: impaired control, social impairment, risky use, and tolerance/withdrawal. Roughly 30% of users meet criteria for current CUD; risk is dose- and duration-dependent (Hasin et al., 2018).

Withdrawal symptoms (occurring after abrupt cessation after regular use) include:

• Irritability, anxiety, sleep disturbances
• Decreased appetite, restlessness
• Physical symptoms: headache, shakiness, sweating

Symptoms peak at days 2–3 and resolve within 1–2 weeks (longer in adolescents) (Grundmann et al., 2018).

Clinical note: Medical cannabis at therapeutic doses—particularly high-CBD/low-THC formulations—shows lower abuse liability than recreational products (Volkow et al., 2016).

Best Practices for Clinical Use
Medical cannabis should be considered a last-line or adjunctive therapy after conventional treatments fail. Key principles include:

1. Individualized dosing: Start low (e.g., ≤2.5 mg THC), go slow; favor CBD-dominant or balanced THC:CBD ratios.
2. Route selection: Oral/inhaled for systemic effects; topical/sublingual for localized relief.
3. Monitoring: Assess efficacy, side effects, and signs of CUD at each visit.
4. Counseling: Disclose risks (especially for vulnerable populations) and emphasize evidence-based alternatives.

Conclusion
Medical cannabis demonstrates therapeutic value for specific conditions—particularly chemotherapy-induced nausea, MS spasticity, and treatment-resistant epilepsy—but requires rigorous risk-benefit assessment. As global policies evolve toward evidence-based regulation, clinicians must stay updated on pharmacology, legal frameworks, and emerging data to ensure patient safety and optimal outcomes.

References (Selected)

• National Academies of Sciences, Engineering, and Medicine. (2017). The Health Effects of Cannabis and Cannabinoids.
• Whiting, P.F., et al. (2015). JAMA, 314(18), 1836–1849.
• Devinsky, O., et al. (2017). The New England Journal of Medicine, 376(21), 2011–2020.
• Hasin, D.S., et al. (2018). JAMA Psychiatry, 75(4), 349–357.
• Volkow, N.D., et al. (2016). The New England Journal of Medicine, 375(16), 1547–1552.
• CDC. (2020). MMWR, 69(36), 1197–1202.
• UNODC. (2022). World Drug Report 2022.

Note: This review is for informational purposes only and does not constitute medical advice.