The concept of cannabis tolerance is quite interesting. Now that patients are using preparations that contain different prominent cannabinoids, including delta-9-tetrahydrocannabinol (THC), cannabidiol (CBD), tetrahydrocannabinolic acid (THCA), cannabidiolic acid (CBDA), and cannabinol (CBN), the question of tolerance no longer relates to THC only.
Tolerance is defined as the need to use more of a drug to get the desired effect. Stated another way, less of an effect is achieved with a previously effective amount. It is clear that tolerance to THC develops following repeated exposure. How much exposure is needed to develop tolerance appears to be different for each person. Animal research in the 1990s suggested that tolerance developed due to a reduction of cannabinoid receptors in the brain after they were exposed to chronic THC.