Cannabis is the common name for a few plants in the cannabis genus, including sativa, indica, and ruderalis. It is primarily used for its psychoactive properties around the world. Cannabis has also been traditionally used to treat inflammatory disorders and is increasingly being used in modern medicine.
Cannabis' primary active chemical, Δ9THC, or delta-9 tetrahydrocannabinol, acts on the cannabinergic system in the body, which is actually named cannabis after the plant. This system is regulated by two receptors, called cannabinoid receptor type 1 (CB1) and cannabinoid receptor type 2 (CB2). CB1 is responsible for most of the psychoactive effects of cannabis, and CB2 is responsible for many of the long-term benefits cannabis may provide for inflammation and related diseases.
THC and CBD appear to be notable analgesics and can reduce pain in a variety of health conditions. Pain in multiple sclerosis and neuropathic pain, in general, have the best evidence for benefits, and they also appear to be useful in cancer, fibromyalgia, rheumatoid arthritis, and pain from wounds. However, more research on those is needed. There is great interest in using cannabis to reduce opioid use, and while some evidence supports this, more research is needed to determine where it may be most effective. In instances of severe pain, the reduction in pain may not be enough to reduce opioid use.
Inhaling cannabis smoke increases diastolic blood pressure and heart rate, though this change is temporary. However, many case studies note cannabis usage 30 – 60 minutes before heart attacks, so it's possible that this acute effect could be dangerous for those at high risk. Heart attacks can occur when people with an elevated risk for heart disease push their blood pressure and heart rate to dangerous levels. It may also interact with some pharmaceuticals, which could result in elevated blood pressure and a heart attack. Smoking cannabis has also been associated with bronchitis.
Cannabis usage over a long period of time can cause tolerance and subsequently withdrawal. Cannabis withdrawal is recognized by the Diagnostic and Statistical Manual of Mental Disorders (DSM-5). On a molecular level, cannabis tolerance occurs when the CB1 receptor is overstimulated and internalized, meaning absorbed by the cell. The CB1 receptor and the N-methyl-D-aspartate receptor (NMDA) receptor are linked when it comes to cannabis, so when CB1 signaling is inhibited, NMDA signaling is also hampered. This may cause cannabis to be less effective for treating epilepsy and schizophrenia, though it also reduces the memory loss associated with cannabis use. Tolerance does not significantly affect the CB2 receptor, so cannabis may be effective for inflammatory disorders over a longer period of time.
Originally, this page included various studies on isolated THC. We have decided to transition the Human Effect Matrix of this page to one that exclusively includes studies on combinations of THC and CBD, either in the form of whole cannabis leaf, cannabis oil, or pharmaceutical combinations of THC and CBD. We have a dedicated CBD page and hope to release a dedicated THC page in the not-too-distant future.
In one sense, this should provide us a better way to understand the expected effects of different products. On the other hand, because a large amount of clinical research is in isolated and synthetic THC, this page by itself is insufficient, in a sense. Various painful conditions that respond to isolated THC could also benefit the same dose of THC from whole cannabis or a THC/CBD product, as the addition of CBD or the other parts of cannabis will be unlikely to counteract those effects; if anything CBD appears to be a notable analgesic in its own right. So when you're using this page, know that there's a good chance that there is more research on isolated THC or CBD for various outcomes (especially chemotherapy side-effects).
This page is also incomplete because we have omitted some research that we didn't find to be particularly useful for this page. This included a vast literature on the psychological and cognitive effects of cannabis, largely when taken acutely. It also included various studies on health conditions where there were very few applicable studies, though these will be added next update.