Hemp - as a drug

Until the late 19th century, hemp - then known as hashish - was only used as a medicine in Europe and North America. The history of its rise as a recreational drug - to some extent replacing opium - is complex. It is closely connected to its promotion by some doctors, and to influences from North Africa (in Europe) and Mexico and South America (in North America). By the 1930s, hashish consumption had been prohibited in many countries, as part of a general drive against drugs.

A controversial drug

Since the beginnings of hashish use in the West, there have been vigorous disputes as to the safety of hashish use, particularly as compared to the use of opiates such as morphine or cocaine. These disputes have gathered pace since hashish use started to expand in the 1960s, when terms such as marijuana, weed and grass became popular. In 2004 the UK government reclassified marijuana as a class C drug, in recognition that its effects are less harmful than those of Class B drugs such as amphetamines. There is increasingly strong evidence that heavy or long-term use of marijuana can lead to mental and physical health problems. In the light of this, the campaign for decrimilisation of marijuana is unlikely to be successful.

Active compounds

The main psychoactive ingredient in hemp is a cannabinoid compound, delta-9-tetrahydrocannabinol, or 'THC'. Local forms of hemp vary a great deal in their THC content, and forms that are virtually THC free have been bred for fibre production. Hemp smoke contains more than 150 other compounds, many of which have a role in its psychoactive and medicinal properties, and some of which are responsible for its damaging properties. THC copies the actions of receptors in the brain called 'neurotransmitters' and interferes with normal functions. The brain contains a compound known as anandamide, which has similar effects on the body as THC. THC mimics anandamide and bonds to the same receptors.