THC (Tetrahydrocannabinol): Effects, Research and Risks

Urgent first: children and edibles

Children eating cannabis edibles such as gummies is a growing health concern. It usually happens by accident and can result in hospitalization and serious illness. [1] The FDA says that if you reasonably suspect a child swallowed a cannabis product, take the child to a physician or emergency department, especially if the child acts unusually or feels sick. [2] In the US, call Poison Help at 1-800-222-1222 or 911 for an emergency; see Poison Help by country and what to do first in poisoning.

Overview and classification

THC (delta-9-tetrahydrocannabinol) is the part of cannabis that produces the "high." [3] Delta-9 THC is the most abundant form of THC in the plant, and it can temporarily change mood, thoughts and perception. [1] It acts on the body's CB1 and CB2 cannabinoid receptors; a review describes THC and CBD as partial agonists (partial activators) or antagonists there. [4] Two lab-made THC-related medicines are FDA-approved, but the plant itself is not approved for any medical use. [5]

Evidence labels used: approved medicine, promising but limited, mixed, insufficient evidence, evidence of harm.

Regulatory category

Effects: what people report and what research finds

• Short-term. Cannabis can make people happier or more relaxed, and can alter time perception and impair thinking, memory and body movement. It can also cause irritability, restlessness, increased appetite and a faster heart rate. [1]
• Anxiety, fear or panic. These are more likely with a large amount, a strong product, or little experience. [1]
• What changes the effect. NIDA lists the amount, THC potency, other ingredients, how it is taken, other drugs, medical conditions, age, sex, genes and prior experience. [1]
• Timing. In a pharmacology review, inhaled THC acted within seconds to minutes and tapered over 2 to 3 hours, while swallowed THC started after 30 to 90 minutes and lasted about 4 to 12 hours. [6] This delay matters. NIDA says people may use more of an edible because effects take longer. [1]

Research by use

For more, see clinical research overview and approved cannabinoid medicines.

Risks and adverse effects

Label: evidence of harm for the items below, with NIDA noting where more research is needed.

• Lungs. Cannabis smoke contains many toxins, irritants and carcinogens like tobacco smoke; long-term smoking is linked to chronic bronchitis and other airway problems. [1] The FDA has warned people not to use vaping products that contain THC. [5]
• Mind and mental health. Frequent or heavy use is linked to problems with learning, memory and attention. Some evidence links use to earlier onset of psychosis in people at genetic risk, and to depression in adolescents. [1]
• Heart. Heart rate and blood pressure rise right after use; long-term links to stroke, heart attack and arrhythmia are not settled. [1] Cannabis may also cause dizziness on standing, raising the danger of falls. [5]
• Cannabis use disorder. Studies estimate 22 to 30 percent of people who use cannabis have it, and higher THC concentrations are linked to a greater chance of progressing to it. [1] Treatments are behavioral; no medicine is approved for it. [1]
• Stomach. Cannabinoid hyperemesis syndrome is repeated nausea, vomiting and abdominal pain after long-term heavy use; it resolves only when use stops completely. [1]
• Driving. Studies suggest cannabis may affect driving, and it is the drug most often found in the blood of drivers in crashes. [1] See pregnancy, teens and driving.
• Delta-8 and similar products. The FDA has not approved delta-8 THC for safe use and has received adverse event reports. [7] See minor cannabinoids.

Special groups

• Pregnancy and breastfeeding. Use is linked with lower birth weight and preterm birth; ACOG recommends counseling against use when trying to get pregnant, during pregnancy and while breastfeeding. [1]
• Teens. Regular heavy use in adolescence is linked to poorer working memory and academic functioning. [1]
• Older adults. Use has risen fastest in adults over 50, and cannabis may interact with warfarin, opioids and benzodiazepines. [1] See medication interactions.