Cannabis sativa grows freely in tropical region. Marijuana is the name given to the dried leaves and flower heads, prepared as a smoking mixture. Cannabis extracts contain numerous related compounds. The most abundant cannabinoids are THC, its precursor cannabidiol and cannabinol. THC is the most active pharmacologically, and also the most abundant.

THC acts mainly on the CNS. The main subjective effects in human consist of:

• a feeling of relaxation and well being, similar to the effect of ethanol, but without the accompanying aggression.
• a feeling of sharpened sensory awareness, with sounds and sights seeming more intense and fantactic.

These effects are similar to, but usually less pronounced that, those produced by phycchotomimetic drugs such as LSD. Subjects report that time passes extremely slowly. The alarming sensations and paranoid delusions that ofter occur with LSD are seldom experienced after cannabis.

Central effects that can be directly measured in human and animal studies include:

• impairmet of short-term memory, and simple learning tasks- subjective feeling of confidence and heightened creativity are not reflected in actual performance.
• impairment of motor coordination.
• catalepsy.
• the retention of fixed unnatural postures.
• analgesia.
• antiemetic action.
• increased appetite

The main peripheral effects are cannabis are:

• tachycardia.
• vasodilatation.
• reduction of intraocular pressure.
• bronchodilatation.