Risks & Responsible Use

A medication that does nothing has no side effects. The fact that cannabis can produce meaningful effects also means it can produce unwanted ones. The goal of this page isn't to scare you off — it's to give you the same information your physician will discuss with you, so the conversation starts from a real understanding.

Common side effects

Most side effects are mild and dose-related. The most common include:

• Dry mouth and dry eyes. Annoying but harmless.
• Dizziness or lightheadedness, especially when standing up quickly. More common in older adults and at higher THC doses.
• Sleepiness or fatigue. Often the desired effect at night, sometimes a problem during the day.
• Increased heart rate. Usually short-lived but worth discussing if you have heart disease.
• Anxiety or paranoia — especially with higher THC doses, edibles taken on an empty stomach, or in patients new to cannabis.
• Cognitive slowing — short-term memory, attention, reaction time. Usually resolves as the dose wears off.
• Cannabinoid hyperemesis syndrome in long-term, heavy users — repeated cycles of severe vomiting that resolve only when cannabis is stopped completely.

Drug interactions to know

Cannabis interacts with several common medications through the liver's CYP450 enzyme system. The most clinically important interactions include:

• Blood thinners (especially warfarin): Cannabis can increase bleeding risk. INR monitoring may need to be more frequent.
• Sedatives and benzodiazepines: Additive sedation — may cause excessive drowsiness or impaired breathing.
• Opioid pain medications: Combined effects can be unpredictable. Some patients reduce opioids successfully; others experience excessive sedation.
• Certain antidepressants and antipsychotics: May increase or decrease blood levels of either medication.
• Anti-seizure medications: CBD specifically can change blood levels of clobazam, valproate, and others.
• Immunosuppressants and chemotherapy: Always discuss with your oncologist or transplant team before starting.

Mental health considerations

Cannabis is not the right choice for everyone, and mental health is one of the most important areas to think carefully about:

• Personal or family history of psychotic disorders. THC-containing products can trigger or worsen psychosis in vulnerable individuals. Patients with schizophrenia or a strong family history should avoid THC.
• Severe anxiety or panic disorder. THC can paradoxically worsen anxiety — especially at higher doses. Lower-THC or CBD-dominant preparations may be more appropriate if cannabis is considered at all.
• Bipolar disorder. Cannabis can destabilize mood and interfere with mood-stabilizing medications.
• History of substance use disorder. Cannabis use disorder is real — roughly 9% of adults who use cannabis develop problematic use. Honest conversation with your provider matters.

Driving, work, and impairment

THC impairs reaction time, judgment, and motor coordination. Driving under the influence of cannabis is illegal in every U.S. state regardless of medical certification. Even if you don't feel impaired, you may still test positive and may still be legally impaired.

• Never drive within at least several hours of inhaled THC, or within 6–8+ hours of an edible.
• Many employers — including federal employees, commercial drivers, healthcare workers in some roles, and safety-sensitive positions — enforce zero-tolerance policies regardless of state law.
• Medical certification does not protect you from job-related drug testing in most workplaces.
• Discuss your specific work situation with your physician before starting.

Safe storage at home

Edibles in particular can look like ordinary candy or baked goods. Treat cannabis the same way you'd treat a prescription opioid:

• Store in original child-resistant packaging, in a locked cabinet whenever possible.
• Keep out of sight and out of reach of children, pets, and visitors.
• Never transfer to unmarked containers — you (or someone else) may confuse dose or contents.
• Pediatric exposures from accidentally eaten edibles are a leading cause of cannabis-related ER visits in legalized states. This is preventable.
• When traveling: medical cannabis is still federally illegal and cannot legally cross state lines.

Responsible-use principles

If your physician determines cannabis is appropriate for you, a few principles consistently separate good outcomes from bad ones:

• Start low, go slow. Begin with the lowest reasonable dose, especially with edibles. Wait at least 2 hours before re-dosing an edible — they're slow to take effect and easy to overdose by re-dosing too soon.
• Document what works. Keep a simple log: product, dose, time, effect, side effects. This helps your physician fine-tune your plan.
• Don't mix with alcohol, especially when you're new to a product. The combination amplifies impairment.
• Take breaks. Tolerance builds quickly. Periodic breaks restore effectiveness.
• Choose your modality with intent. Inhaled = fast on, fast off (good for breakthrough symptoms). Edibles = slow on, long duration (good for sustained relief). Tinctures and capsules sit between the two.
• Follow up regularly. Your plan should evolve. Don't hesitate to tell your provider what's not working.

When to stop and call your provider

Reach out to your medical team — or seek emergency care — for any of the following:

• Chest pain, severe shortness of breath, or fainting.
• Severe vomiting that won't stop (especially recurring episodes — see cannabinoid hyperemesis syndrome above).
• Hallucinations, severe paranoia, or thoughts of harming yourself or others.
• A new medication added by another doctor — always recheck for interactions.
• Anything that feels like "this isn't working anymore" or "this is making me worse." Your plan should adapt.