Hash is an extracted cannabis product composed of compressed or purified preparations of stalked resin glands, called trichomes, from the plant. It is defined by the 1961 UN Single Convention on Narcotic Drugs (Schedule I and IV) as "the separated resin, whether crude or purified, obtained from the cannabis plant". The resin contains ingredients such as tetrahydrocannabinol (THC) and other cannabinoids—but often in higher concentrations than the unsifted or unprocessed cannabis flower. Purities of confiscated Hashish in Europe (2011) range between 4-15%. Between 2000 and 2005 the percentage of hashish in cannabis end product seizures was at 18%.
Hashish may be solid or resinous depending on both preparation and room temperature; pressed hashish is usually solid, whereas water-purified hashish—often called "bubble melt hash"—is often a paste-like substance with varying hardness and pliability; its color, most commonly light to dark brown, can vary from transparent to yellow, tan, black, or red. This all depends on the process and amount of solvent left over.
Besides its recreational use, the active ingredient of hashish, THC, has been of interest for research and medical purposes since its arrival in the 18th century. While it was widely used as a medicine for multiple diseases, the emergence of specific treatments led to a sharp decline in prescriptions, eventually becoming illegal to use via the 1971 UN Convention on Psychotropic Substances.
The street price for hashish in Europe in 2011 varied from €3 (Portugal) per gram to €18 in Malta, or even as high as 200NOK (€20/$25) in Norway.