What is a safe amount of cannabis (tetrahydrocannabinol) use for a patient with a history of substance use and potential eligibility for lung cancer screening?

There Is No "Healthy" Amount of Cannabis Use

For patients with substance use history who may be eligible for lung cancer screening, cannabis use should be strongly discouraged due to documented risks of addiction, respiratory harm, potential lung cancer association, and interference with cancer screening eligibility criteria. 1

Critical Risks in This Population

Substance Use Disorder Development

• 10% of adults with chronic cannabis use develop cannabis use disorder, characterized by using more than intended and difficulty cutting back 1
• Patients receiving medical cannabis cards have nearly twice the incidence of developing cannabis use disorder (17% vs 9%) within 12 weeks compared to controls 1
• Your patient's history of substance use places them at substantially elevated risk for developing cannabis dependence 1

Respiratory and Cancer Concerns

• High-dose cannabis use (>4 times per week for over a year) can cause cannabinoid hyperemesis syndrome, mimicking cyclic vomiting 1
• While evidence linking cannabis to lung cancer remains conflicting and confounded by tobacco co-use, no clear evidence demonstrates that cannabis inhalation is safe from lung cancer risk 1
• A 40-year Swedish cohort study found "heavy" cannabis use (>50 lifetime uses) associated with more than twofold increased lung cancer risk (HR 2.12,95% CI 1.08-4.14) even after adjusting for tobacco use 2
• Cannabis smoking doubles the risk of developing lung cancer according to French respiratory medicine guidelines 3
• Low-strength evidence suggests marijuana smoking is associated with testicular germ cell tumors, with >10 years use showing OR 1.36 (95% CI 1.03-1.81) 4

Impact on Lung Cancer Screening Eligibility

• Cannabis use is NOT considered a qualifying risk factor for lung cancer screening under any current guideline 5
• Screening eligibility requires ≥20 pack-years of cigarette smoking (not cannabis), age 50-80 years, and current smoking or quit within 15 years 1, 5
• Cannabis exposure alone does not meet USPSTF, NCCN, or American Cancer Society criteria for screening 1, 5

Cardiovascular and Psychiatric Risks

• Cannabis smoking may be associated with myocardial infarction, stroke, and new-onset arrhythmias 1
• Cannabis use may be associated with increased risk for developing depressive disorders and may exacerbate psychiatric conditions in vulnerable individuals 1
• Early onset cannabis use, especially weekly or daily, strongly predicts future dependence 1

Motor Vehicle Safety

• Cannabis users are more than twice as likely to be involved in motor vehicle crashes compared to non-users 1
• This risk compounds with the patient's substance use history 1

Specific Dosing Concerns

CBD Products

• Clinicians should not recommend ≥300 mg/day of oral CBD due to lack of proven efficacy and risk for reversible liver enzyme abnormalities 1
• No cases of drug-induced liver injury were reported with CBD doses <300 mg/day 1
• Monitoring liver enzymes with CBD use is important in clinical settings 1

THC Products

• No safe threshold for THC use has been established in guidelines 1
• Average THC concentration in cannabis plants nearly doubled from 9% (2008) to 17% (2017), with concentrates reaching 70% THC 1
• High doses of THC may be associated with psychosis 1

Clinical Recommendation Algorithm

For your patient with substance use history:

1. Advise complete cannabis abstinence given addiction risk and lack of established safe dose 1

2. If patient reports current cannabis use:

   • Screen for cannabis use disorder symptoms (using more than expected, difficulty cutting back) 1
   • Counsel on withdrawal symptoms if cessation attempted (irritability, restlessness, anxiety, sleep disturbances lasting up to 14 days) 1
   • Refer to substance use treatment if cannabis use disorder identified 1

3. For lung cancer screening eligibility:

   • Assess cigarette smoking history only (cannabis does not count toward pack-years) 1, 5
   • Patient qualifies if age 50-80 years with ≥20 pack-years cigarette smoking, currently smoking or quit within 15 years 1, 5
   • Alternative NCCN criteria: age ≥50 years with ≥20 pack-years plus one additional risk factor (personal cancer history, chronic lung disease, first-degree relative with lung cancer, occupational carcinogen exposure, radon exposure) 5

4. Provide vigorous smoking cessation counseling for both cannabis and tobacco as the single most effective intervention to reduce lung cancer risk 5

Common Pitfalls to Avoid

• Do not equate cannabis smoking with cigarette smoking for screening eligibility - only cigarette pack-years count 1, 5
• Do not assume cannabis is "safer" than tobacco - marijuana smoke contains polycyclic aromatic hydrocarbons and carcinogens at higher concentrations than tobacco smoke 3
• Do not recommend cannabis for symptom management outside specific refractory chemotherapy-induced nausea/vomiting in cancer patients who have failed optimal antiemetic prophylaxis 1
• Do not ignore the patient's substance use history when counseling about cannabis - this substantially elevates addiction risk 1