Cannabis can cause unwanted effects even when someone uses it for a medical reason. These can range from dry mouth and dizziness to severe confusion or repeated vomiting. The product, THC amount, route, other substances and a person’s health all matter. This guide explains what to watch for, when to seek help and what to discuss with a healthcare professional.
Updated October 4, 2026. Educational information; not a diagnosis or a personal dosing plan.
When to get help
In the United States, call Poison Control at 1-800-222-1222 if someone may have used too much cannabis. Call 911 for an emergency. Severe confusion, hallucinations, panic or severe vomiting deserve prompt attention. Do not drive yourself for care. The CDC’s cannabis FAQ explains the signs of overconsumption and where to get help.
If a child may have swallowed a cannabis product, contact Poison Control promptly rather than waiting for symptoms. Keep the package available so you can describe what was taken.
What side effects can cannabis cause?
Health Canada’s consumer guidance lists immediate effects that can include:
- Dry mouth, red eyes or increased appetite.
- Dizziness, feeling faint, drowsiness or a faster heart rate.
- Changes in attention, memory and thinking.
- Anxiety, panic or paranoia.
Not everyone experiences the same effects, and a familiar product can feel different on another occasion. An effect being common does not mean you have to tolerate it. Tell your clinician about symptoms that interfere with work, sleep, movement or daily activities.
Why timing and product type matter
Edibles can take 30 minutes to 2 hours to produce noticeable intoxication and may last longer than expected. The CDC’s edible-cannabis guidance explains why taking more before the first amount has taken effect can lead to overconsumption. A product’s serving size is not an individualized recommendation.
Check the THC and CBD amounts and the intended route. Our tincture label and timing guide explains the difference between liquid volume and cannabinoid content. Do not use a time estimate as proof that you are safe to drive.
Risks with repeated use
The CDC’s health-effects overview describes risks including impaired driving skills, harm to lung tissue from smoking, and difficulty controlling cannabis use. Continuing despite problems or repeatedly being unable to cut down is a reason to seek support, not a personal failing.
Repeated episodes of nausea, vomiting and abdominal pain can also occur with cannabinoid hyperemesis syndrome. The American Gastroenterological Association provides clinical guidance on CHS. Vomiting has many possible causes; tell a clinician about cannabis use so they can assess it alongside other explanations. Do not assume that more cannabis will relieve it.
Mental health and younger people
Cannabis can cause anxiety, disorientation and paranoia. The CDC describes an association between cannabis use and psychosis, with a stronger association for earlier and more frequent use. An association does not establish the cause of an individual person’s illness, but it belongs in a discussion of personal and family mental-health history.
Keep products in their original child-resistant packaging, locked away from children and pets. Label homemade edibles clearly and store them separately from ordinary snacks.
Does CBD have side effects?
Yes. CBD’s lack of a characteristic THC high does not make it risk-free. The FDA flags liver injury, drug interactions and drowsiness among its concerns. Bring CBD products to the same medication review as THC products. Our medication-interactions guide explains what information to gather.
Cannabis withdrawal deserves attention
Withdrawal can happen after reducing or stopping regular cannabis use. Symptoms can include irritability, anxiety, cravings, reduced appetite and sleep problems. These symptoms appear in the withdrawal checklist hosted by the National Institute on Drug Abuse. Their impact varies, and they should not be dismissed as “not that bad.”
If sleep or mood changes are difficult
Ask a healthcare professional for support with a plan to reduce or stop use. Describe how much and how often you use cannabis, other substances or medicines, and changes in sleep, mood and appetite. Do not add alcohol or change prescribed sleep medicines to manage symptoms on your own.
An effect can help one person and trouble another
Increased appetite or sleepiness may be welcome in one situation and disruptive in another. That does not make cannabis a universal treatment for poor appetite or sleep. Discuss the underlying problem and the evidence for the specific treatment being considered.
What to bring to your next appointment
- The product label, including THC and CBD amounts and how it is used.
- The measured amount, time used and when symptoms began.
- A complete list of medicines, supplements and other substances.
- The benefit you hoped for, what actually changed and any unwanted effects.
Tell your clinician if you are pregnant, planning a pregnancy or breastfeeding. The FDA advises avoiding cannabis, including THC and CBD, during pregnancy and breastfeeding; your care team can help you find alternatives for the symptoms you are trying to manage.
Separate access from treatment decisions
A medical card does not remove side-effect risks. Our medical cannabis overview explains the difference between state access programs, products and a treatment plan. If your question is about eligibility or application steps, start with the medical card guide.
