Cannabis Strains that is considered to have a THC content in excess of 20% which is very high and will be very potent. Cannabis strains with high THC content can have a very powerful effect on the mind. This can be desirable and undesirable depending on the individual marijuana users needs. THC is the main active compound in marijuana and Strains with high content are likely to be more psychoactive and hypnotic and can be known for being a little trippy. Be careful if you are a novice as high THC cannabis can have severe adverse effects.