The most researched cannabinoid is delta-9-tetrahydrocannabinol (THC). THC is responsible for the way your brain and body respond to cannabis, including the high and intoxication. THC has some therapeutic effects but it also has harmful effects. Harmful effects may be greater when the strength of THC is higher. The potency (concentration or strength) of THC in cannabis is often shown as a percentage of THC by weight (or by volume of an oil). THC potency in dried cannabis has increased from an average of 3% in the 1980s to around 15% today. Some strains can have an average as high as 30% THC. Cannabis that contains very low amounts of THC in its flowers and leaves (less than 0.3%) is classified as hemp.
Cannabidiol (CBD) is another cannabinoid. Unlike THC, CBD does not produce a high or intoxication. There is some evidence that CBD may block or lower some of the effects of THC on the mind. This may occur when the amount of CBD in the cannabis is the same or higher than the amount of THC. CBD is also being studied for its possible therapeutic uses.