Variation in the THC content in illicitly imported Cannabis products.

The tetrahydrocannabinol (THC) content of 304 seizures of illicit Cannabis products was determined using gas chromatography. This procedure results in the conversion of THC acid to THC itself and thus gives the total THC content of the material, which reflects its potency as experienced by the smokers. The study was carried out over three years, thus enabling comparisons to be made between THC levels from a given country of origin over this time span in addition to any variations between the countries. In the early part of the study, herbal cannabis from South East Asia was consistently the best quality and that from the Caribbean the poorest quality. In the third year of the study, the material from South East Asia was in general no richer in THC than material from other areas of the world. Cannabis resins normally had higher THC contents than most herbal material, but the highest levels were found in "hash oil" from the Middle East and the Indian subcontinent.