Variation in the THC content of illicitly imported Cannabis products--1984-1989.

The tetrahydrocannabinol (THC) content of more than 180 samples of fresh illicit Cannabis products, seized by H.M. Customs and Excise on entry into Great Britain and Northern Ireland over the period 1984-1989, has been determined by gas chromatography. The average THC content of herbal cannabis remained high due to good quality cannabis from Jamaica and the USA, but that of cannabis resin was slightly lower. Resin from Morocco has changed significantly in its physical appearance. There was no fresh seizure of cannabis oil in this period.