Although cannabis contains over 400 different chemicals, the main ingredient which affects the mind is THC. The amount of THC in the hemp plant determines the strength of the drug. The weather, soil and other factors determine the percentage of THC found in the plant. By using modern farming techniques, hemp growers have developed strains of cannabis which have much higher levels of THC than in the past. THC levels averaged 1% in 1974 and 4% in 1994. In 2008, levels reached 9.6%, highest ever since analysis of the drug began in the 1970s.
One form of cannabis, called sinsemilla (Spanish for “without seeds”), may have THC levels from 7.5% to as much as 24%.