Medical Cannabis Safety, Side Effects & Interactions

Medical cannabis can be an effective treatment for various conditions, but like any medicine, it comes with potential side effects and interactions. Understanding these risks, knowing how to use cannabis safely, and consulting a specialist can help you get the most benefit while reducing harm.

Common Side Effects

Medical cannabis affects the body in multiple ways. Side effects can be mental, physical, or cognitive, and may vary depending on the THC and CBD content of the product.

Mental / Psychological

  • Dizziness, confusion, feeling “high”
  • Anxiety, paranoia, hallucinations
  • Worsening of pre-existing mental health symptoms

Physical

  • Increased heart rate
  • Dry mouth, nausea, vomiting, diarrhea
  • Changes in appetite
  • Weakness and fatigue

Cognitive

  • Memory and attention problems
  • Slower reaction times
  • Difficulty with complex thinking or concentration

Reference: NHS – Cannabis-Based Products for Medicinal Use

Serious Side Effects & Risks

Although less common, high-THC or improperly dosed cannabis products can cause serious complications:

  • Cardiovascular: Risk of heart attack, stroke, or unstable heart rhythm, especially in patients with pre-existing heart conditions
  • Mental Health: Potential trigger for mania, psychosis, or depression in susceptible individuals
  • Liver: CBD can affect liver function and interact with other medications metabolized by the liver
  • Reproductive: Animal studies suggest possible harm to male fertility
  • Dependence: Some patients may develop cannabis use disorder
  • Reference: Medicines and Healthcare products Regulatory Agency (MHRA)

Interactions with Other Medications

Cannabinoids can affect the metabolism of other drugs, sometimes leading to increased side effects or reduced effectiveness:

  • Other medications: CBD and THC may alter absorption or metabolism of prescription drugs
  • Alcohol & sedatives: Combining cannabis with alcohol or CNS depressants can cause extreme drowsiness
  • Antipsychotic medications: Interactions can be complex; always consult a specialist
  • Reference: National Institutes of Health (NIH) – Cannabinoid Drug Interactions

Specific Populations & Considerations

Some groups should be particularly cautious or avoid medical cannabis altogether:

  • Adolescents: Avoid use due to effects on brain development
  • Pregnant or breastfeeding individuals: Cannabis can harm the developing baby
  • Pre-existing conditions: Cardiovascular disease or severe mental health disorders increase risk
  • Product labeling: Always check THC/CBD levels; some over-the-counter CBD products may contain higher THC than stated

Safety Tips for Patients

  • Consult a specialist: Discuss your medical history and all medications before starting
  • Start low, go slow: Begin with the lowest effective dose and increase gradually
  • Avoid driving or machinery: Cannabis can impair memory, reaction time, and judgment
  • Report side effects: Notify your doctor and report serious adverse effects through the Yellow Card Scheme

Learn More

If you’re considering medical cannabis, speak to a specialist at Medcann Pharmacy for guidance on safe and effective treatment options.