11-Hydroxy-Δ9-tetrahydrocannabinol (11-OH-THC) is the main active metabolite of Tetrahydrocannabinol (THC) which is formed in the body after cannabis is consumed. The conversion from THC to 11-OH-THC is relatively high when cannabis is consumed in the form of cannabis edibles and, compared to oral consumption, lower when it is smoked or vaped. 11-OH-THC is more potent than THC and crosses the blood–brain barrier more easily. 11-Hydroxy-THC has been shown to be active in its own right. This might partially explain the biphasic effects of cannabis, whereby some effects such as increased appetite tend to be delayed rather than occurring immediately when the drug is consumed.
Fresh cannabis contains Tetrahydrocannabinolic acid (THCA), which is converted into THC after heating and then metabolized by the body into 11-Hydroxy-THC. Peak THC concentrations are lower after eating/drinking cannabis than after administration by smoking or vaping, but conversely, 11-OH-THC/THC ratios are higher after eating/drinking than after smoking cannabis. After administration through eating or drinking, approximately equal quantities of THC and 11-OH-THC are formed, whereas 11-OH-THC is a minor constituent after administration by intravenous or smoking routes. Because edible doses are processed by the liver before entering the bloodstream, THC consumed as edibles produces high levels of 11-OH-THC, while smoked cannabis, which goes directly from the lungs to the brain via the bloodstream and does not enter the liver, produces lower levels.
11-Hydroxy-THC is subsequently metabolised further to 11-nor-9-carboxy-THC, which is not psychoactive but might still play a role in the analgesic and anti-inflammatory effects of cannabis.