Tetrahydrocannabinol (THC) is one of the major active cannabinoids found in cannabis. It is the main compound responsible for the psychoactive effects of cannabis, including changes in mental processes (e.g., thoughts, mood, and perception) that cause the feeling of being “high”.^[3] While THC is found naturally in cannabis in combination with many other active compounds, like cannabidiol (CBD), some supplements and prescription medications contain isolated THC or synthetic THC analogs, which will be the focus of this page.

THC may have some therapeutic benefits on pain and chemotherapy-induced nausea and vomiting. Despite these potential benefits, THC can induce intoxication and cause other side effects that may reduce the quality of life for some people.^[4][5] On the flip side, some people seek out THC recreationally for its intoxicating effects, which can include euphoria, a sense of relaxation, and altered sensory perception.

THC is likely effective for reducing nausea and vomiting in children and adults undergoing chemotherapy. The effects are superior to a placebo and potentially comparable to standard treatments, although more research is needed to confirm the latter.^[6][7] While THC might reduce nausea and vomiting in other contexts, this hasn’t been thoroughly researched.

THC may also reduce chronic pain to a small or moderate degree, with most research looking at neuropathic pain of various origins.^[8][9] Limited research suggests that THC may also reduce pain due to cancer or multiple sclerosis.^[10] Still, how THC compares to commonly used pain relievers is not particularly clear, and when used alongside opioid analgesics, THC doesn’t seem to reduce the required dose of opioids.^[11][12]

THC is associated with a relatively high risk of side effects that tend to be dose-dependent (occurring more often with increasing doses).

The most common side effects of THC include sedation, dizziness, confusion, impaired cognition, impaired coordination, euphoria, anxiety, paranoia, heightened sensory awareness, headache, dry mouth, increased appetite, and nausea. THC can cause intoxication and impair the ability to drive.^[1][13][14]

Less often, THC may cause vomiting, hallucinations, increased heart rate, orthostatic hypotension, and psychosis (in predisposed individuals).^[1] There have also been case reports linking THC with an increased risk of seizure or heart attack.^[15][16][17]

If THC is inhaled via smoking or vaping, it can increase the risk of lung disease or lung injury. Vaporizing THC can minimize the production of potentially cancer-causing compounds formed through combustion; however, there is still a risk of lung injury with vaping.^[3]

THC exerts its effects by interacting with the body’s endocannabinoid system, which involves binding to and activating the cannabinoid receptors cannabinoid receptor 1 (CB1) and cannabinoid receptor 2 (CB2).

The brain and spinal cord are rich in CB1 receptors, which are responsible for most of THC’s effects. When THC activates CB1 receptors, it alters neurotransmission (how neurons communicate) in a way that influences many bodily functions including pain signaling, appetite, cognition, the sleep-wake cycle, and nausea and vomiting. CB2 receptors are found predominantly in immune cells, and their activation by THC may have an anti-inflammatory effect.^[9][18]