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Last Updated: Sunday, 19 June, 2005, 21:26 GMT 22:26 UK
Is it stronger nowadays?
A cannabis cigarette being lit

The story of the cultivation of Cannabis Sativa L, or the hemp plant as it is commonly known, stretches back into antiquity. Although originally produced as a source of fibre - commonly for rope and cloth - its use as a drug, both recreationally and medicinally also has a long history.

For most of this time, it is likely that little changed in the methods used to manufacture the traditional drug products. Recently there have been many in the media and elsewhere in the public domain who have claimed a large increase in the potency of cannabis. These statements have raised concerns that the potency of cannabis may have increased so much that the drug now bears little resemblance to the cannabis that was available some thirty years ago.

The major psychoactive in all cannabis products is Delta 9-tetrahydrocannabinol (THC). It is the concentration of this substance which has traditionally been used to measure the potency of a sample of cannabis. This is the substance that interests the recreational smokers: the higher the level present, the more profound the effect on the user. It's the key element in the "high" experienced by most users.The level of THC is determined by several factors including the genetic make up of the particular strain, the nutrient conditions in which it is grown and most importantly the amount of light the plant receives. When grown under artificial lights an experienced grower can eliminate the vagaries of sunlight and ensure a consistently high level of THC

However, for those whose interest is more medicinal there are other closely-related substances which occur in cannabis, including cannabidiol (CBD) and, in samples that have aged there is cannabinol (CBN). Both CBDs and CBNs have quite different effects to THC. CBD does not have psychoactive properties and seems to regulate the effects of THC when both are present. Research on CBD, although in its early stages, has shown that it may have impact as an anti-psychotic as well as having anti-inflammatory and anti-convulsant properties. Other compounds include the cannabivarins and cannabichromenes; they are all collectively known as cannabinoids.

A distinction is made between cannabis plants for drug use and cannabis grown for fibre. In the EU, cannabis (hemp) cultivated under licence for fibre contains less than 0.3 % THC, and is essentially not usable as a drug. Cannabidiol is often absent in the drug variety of plant but is usually found at levels exceeding 0.5 % in cannabis grown for fibre.

A report by the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) was commissioned in 2004 to specifically examine the validity of these claims about increased potency. The report, entitled "An Overview of Cannabis Potency in Europe", concluded that;

"Statements in the popular media that the potency of cannabis has increased by ten times or more in recent decades are not supported by the limited data that are available from either the USA or Europe. The greatest long-term changes in potency appear to have occurred in the USA. It should be noted here that before 1980 herbal cannabis potency in the USA was very low by European standards." (page 14)

"The natural variation in the THC content between and within samples of herbal cannabis or cannabis resin at any one time and place far exceeds any long-term changes that may have occurred either in Europe or the USA. This natural variation is even greater when material from different geographical locations is examined." (page 15)

"The conclusion of this report is that there have been modest changes in THC levels that are largely confined to the relatively recent appearance on the market of intensively cultivated domestically produced cannabis. Cannabis of this type is typically more potent, although it is also clear that the THC content of cannabis products in general is extremely variable and that there have always been some samples that have had a high potency." (page 16)

The key points of the report which can be found at the EMCDDA website suggested that the changes in average strength of cannabis available may not be as big dramatic as some have claimed.

  • The effective potency in nearly all countries has remained quite stable for many years at around 6-8 %. The only exception has been the Netherlands where, by 2001-2002, it had reached 16 %.
  • The natural variation in the THC content between and within samples of herbal cannabis or cannabis resin at any one time and place far exceeds any long-term changes that may have occurred either in Europe or the USA
  • Herbal cannabis produced by intensive indoor methods (e.g. hydroponic systems with artificial lighting, propagation by cuttings and control of day length) usually has higher THC levels than imported material
  • The higher potency of herbal cannabis produced by indoor methods is a reflection of several factors: genetic, environmental and freshness.

    The natural variation in the THC content between and within samples of herbal cannabis or cannabis resin at any one time and place far exceeds any long-term changes that may have occurred either in Europe or the USA

    The conclusion of this report is that there have been modest changes in THC levels that are largely confined to the relatively recent appearance on the market of intensively cultivated domestically produced cannabis



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