A study of the characteristics of cannabis seeds and the influence of environmental conditions on the content of THC in cannabis plants grown in northern, southern and insular Italy has shown that the fibre-type plants contain mean values of THC in a range from 0.058 to 0.299 per cent. In 1984, the Commission of the European Communities prepared a regulation to prevent diffusion of the drug-type cannabis, providing that raw material could not be imported if its THC content exceeded 0.5 per cent from 1984 to 1987 and after that period the maximum limit would be set up to 0.3 per cent. The concentration of cannabinoids in a cannabis plant depends on genetic factors and on environmental influences such as light, temperature, moisture and oxygen.
Cannabis is mainly smoked and less often inhaled or eaten.
Cannabis smoking or inhalation acts much faster than its oral use. The pharmacologic activity of THC use is usually measured in humans by the effects of such use on the heartbeat frequency, memory, attention, alert state, muscular co-ordination and electroencephalogram. In most cases THC dosage of 3 to 4 mg or higher give rise to significant changes in these parameters. The fibre-type plants are legally cultivated in some regions of the Mediterranean area. During the first year of the project ten species of genetically differentiated hybrids were planted.