Indoor cultivators try to enhance the potency of cannabis through selective breeding and cloning of high-potency cultivars. Indoor cultivation is also used for the selection and isolation of female plants for sinsemilla production. The average THC content of sinsemilla cannabis was about 7.4 per cent in 1994 but some of the seized samples had a THC content of more than 24 per cent. Despite the increasing amounts of cannabis seized by Mexican law enforcement authorities, Mexico remains a supplier of the illicit cannabis markets in the United States. Substantial quantities of cannabis are also smuggled into the United States out of other countries, particularly Colombia, Thailand and, increasingly, Jamaica.
Cannabis remains the most abused illicit drug in the region.
During the last three years, following a continuous decrease from 1985 to 1992, an increase in cannabis abuse among youth has been observed in the United States. This trend is attributed to a decline in the level of perceived risk of abuse, while the actual risk has been increased by the higher potency of the drug. Opium, Heroin Opium poppy is cultivated illicitly in Mexico. The opium produced is used for the illicit manufacture of heroin, which is usually smuggled into the United States. Growing heroin abuse has been reported in Canada, particularly in urban areas.