Cannabis Use
The health effects and risks of marijuana, including smoked, vaped and edible products.
Last revised
Key takeaways
- Cannabis use disorder: about 3 in 10 people who use marijuana have it
- Higher risk: people who start using before age 18 or use it daily
- Most useful single change: Wait for an edible to take effect before taking more.
- Commonest mistake: Driving after using cannabis.
- See a doctor if any of the signs under "When to get help" below apply to you.
Why it matters
Cannabis is legal for adults in many states, but it can still cause dependence, impaired driving and harm to young people and pregnancies.
The numbers, in one place
| Measure | Figure |
|---|---|
| Cannabis use disorder | about 3 in 10 people who use marijuana have it |
| Higher risk | people who start using before age 18 or use it daily |
| Edibles | can take 30 minutes to 2 hours to take effect, which raises the risk of taking too much |
| Pregnancy | no amount is known to be safe during pregnancy or breastfeeding |
| Driving | marijuana slows reaction time and impairs coordination |
What helps
- Wait for an edible to take effect before taking more
- Store all cannabis products locked up and out of children's reach
- Talk to your doctor if you find it hard to cut down
- Call Poison Control at 1-800-222-1222 if a child or pet eats a cannabis product
What to avoid
- Driving after using cannabis
- Using it with alcohol or other drugs
- Using it during pregnancy or while breastfeeding
In depth
Cannabis contains many compounds called cannabinoids. The main one that causes a "high" is THC, which acts on the brain's cannabinoid receptors involved in memory, attention, coordination, appetite and mood. Another, CBD, does not cause a high. Products vary widely, from dried flower and concentrates to vapes, edibles and drinks, and their THC content has generally increased over time, which raises the risk of side effects.
How cannabis is taken changes how it works. Smoking or vaping delivers THC quickly, so effects begin within minutes. Edibles pass through the digestive system and liver, which turns THC into a form that can feel stronger, and effects may not start for up to 2 hours and can last many hours. People who take more because they feel nothing yet are a common source of emergency visits.
State laws on cannabis differ, but legal status does not make it risk-free. Regular use can lead to cannabis use disorder, and heavy use of high-potency products is linked to anxiety, psychosis and, in some people, a severe vomiting illness. Products such as delta-8 THC sold in stores or online may not be regulated or tested, and the FDA has warned about their risks.
Signs and symptoms
- Using more often or in larger amounts than intended
- Trouble cutting down, or strong cravings
- Irritability, trouble sleeping, low appetite or restlessness when not using
- Using despite problems at school, work or in relationships
- Repeated bouts of severe nausea and vomiting that ease with hot showers
- Paranoia, anxiety or unusual thoughts after using
Causes and risk factors
- Starting to use as a teen, when the brain is still developing
- Daily or near-daily use
- High-potency products such as concentrates and many vapes
- Using to cope with anxiety, depression, trauma or sleep problems
- A personal or family history of psychosis or mental illness
- Easy access to cannabis and friends or family who use
How it is checked
Your doctor may ask about cannabis use as part of routine care, especially if you have anxiety, sleep problems, nausea or mood changes. They may ask how often you use, what products you use and whether you have tried to cut down. Cannabis use disorder is diagnosed using the same type of criteria as other substance use disorders, with severity based on the number of symptoms.
For repeated vomiting, your doctor will look for other causes and may consider cannabinoid hyperemesis syndrome, which is linked to long-term regular use. For mental health symptoms, they will ask about family history and other substances. A urine test can detect cannabis but does not show how impaired someone is or how recently they used.
Related topics
- Vaping and Teens: What the Evidence Actually Says (Teen Health)
- What the Guidance Really Says About Medicines and Driving (Medicines Safety)
- The Evidence on Diabetes and Driving, Without the Hype (Diabetes)
- What the Guidance Really Says About Supplements and the Liver (Liver Health)
Where to go next
- Your Questions About Cannabis Use, Answered
- Cannabis Use in Five Minutes
- Substance Use: The Complete Guide
- What the Guidance Really Says About Vaping and E-Cigarettes
- What the Guidance Really Says About Stimulant Use
When to get help
Call 911 if someone has chest pain, severe anxiety or confusion, trouble breathing or is unresponsive after using cannabis, or if a child is very sleepy after eating an edible. See your doctor for repeated severe vomiting linked to regular use.
Where this comes from
- CDC — Cannabis and Public Health
- National Institute on Drug Abuse — Cannabis (Marijuana)
How this page was put together
Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarized or generalized beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.
Medical disclaimer
This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to your doctor, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 911.