The effects of cannabis are caused by chemical compounds in the cannabis plant, including 113 different cannabinoids such as tetrahydrocannabinol (THC) and 120 terpenes, which allow its drug to have various psychological and physiological effects on the human body. Different plants of the genus Cannabis contain different and often unpredictable concentrations of THC and other cannabinoids and hundreds of other molecules that have a pharmacological effect, so the final net effect cannot reliably be foreseen.
Acute effects while under the influence can sometimes include euphoria or anxiety. Although some assert that cannabidiol (CBD), another cannabinoid found in cannabis in varying amounts, may alleviate the adverse effects of THC that some users experience, little is known about CBD effects on humans. Cannabinoid receptor antagonists have previously been tested as antidotes for cannabis intoxication with success, reducing or eliminating the physiological and psychological effects of intoxication. Some of these products are currently in development as cannabis antidotes.
In the United States, medical cannabis research is limited by federal restrictions. Smoking any substance could possibly carry similar risks as smoking tobacco due to carcinogens present in all smoke, and the ultimate conclusions on these factors are disputed.
Cannabis use disorder is defined as a medical diagnosis in the fifth revision of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5).
Chemistry
Cannabinoids and cannabinoid receptors
The most prevalent psychoactive substances in cannabis are cannabinoids, particularly THC. Some varieties, having undergone careful selection and growing techniques, can yield as much as 34% THC. Another psychoactive cannabinoid present in Cannabis sativa is tetrahydrocannabivarin (THCV), but it is only found in small amounts and is a cannabinoid antagonist.
There are similar compounds in cannabis that do not exhibit psychoactive response but are obligatory for functionality: cannabidiol (CBD), an isomer of THC; cannabivarin (CBV), an analog of cannabinol (CBN) with a different side chain, cannabidivarin (CBDV), an analog of CBD with a different side chain, and cannabinolic acid. CBD is believed to regulate the metabolism of THC by inactivating cytochrome P450 enzymes that metabolize drugs; one such mechanism is via generation of carbon monoxide (a pharmacologically active neurotransmitter) by upon metabolism of CBD. THC is converted rapidly to 11-hydroxy-THC, which is also pharmacologically active, so the euphoria outlasts measurable THC levels in blood.
Biochemical mechanisms in the brain
Cannabinoids usually contain a 1,1'-di-methyl-pyran ring, a variedly derivatized aromatic ring and a variedly unsaturated cyclohexyl ring and their immediate chemical precursors, constituting a family of about 60 bi-cyclic and tri-cyclic compounds. Like most other neurological processes, the effects of cannabis on the brain follow the standard protocol of signal transduction, the electrochemical system of sending signals through neurons for a biological response. It is now understood that cannabinoid receptors appear in similar forms in most vertebrates and invertebrates and have a long evolutionary history of 500 million years. The binding of cannabinoids to cannabinoid receptors decrease adenylyl cyclase activity, inhibit calcium N channels, and disinhibit K+A channels. There are at least two types of cannabinoid receptors (CB1 and CB2).
Sustainability in the body
Most cannabinoids are lipophilic (fat soluble) compounds that are easily stored in fat, thus yielding a long elimination half-life relative to other recreational drugs. The THC molecule, and related compounds, are usually detectable in drug tests from 3 days up to 10 days according to Redwood Laboratories. Long-term users can produce positive tests for two to three months after ceasing cannabis use (see drug test).
Toxicities
When cannabis is smoked, blood levels of THC peak rapidly after a few minutes and then decline, although the psychotropic effects persist for longer. Edible forms of cannabis often contain several hundred milligrams of THC, much more than the 32 mg of a typical cannabis cigarette. The rise of edible cannabis products has been responsible for a large increase of poisoning of children and young people: in American states which have legalized cannabis, emergency room admissions of such cases have typically doubled. Symptoms in children can include lethargy, sedation and seizure.