11-Hydroxy-Δ9-tetrahydrocannabinol, abbreviated as 11-OH-THC, is the main active metabolite of THC which is formed in the body after cannabis consumption. 11-Hydroxy-THC has been shown to be active in its own right, but the effects produced are not necessarily identical to those of THC. 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. 11-OH-THC is more potent than THC and crosses the blood–brain barrier more easily.
Peak THC concentrations are lower after oral than smoked administration, but conversely, 11-OH-THC/THC ratios are higher after oral than smoked cannabis. After oral administration, 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 oral doses are processed by the liver before entering the bloodstream, oral THC produces high levels of 11-OH-THC, while smoked cannabis does not.
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.