Hashish is the Arabic word for the resin or thick oily material derived from Cannabis sativa, the hemp plant. The word came into English at the end of the sixteenth century. The hemp resin is usually dried and formed into a wafer or brick. It can also be used to make hashish oil. Other preparations use the resin as well as the flowering tops of the hemp plant. These are called charas in India, esvar in Turkey, anascha in areas of the former Soviet Union, and kif in Morocco and parts of the Middle East.

Tetrahydrocannabinol, or THC, is the major active chemical in products of the hemp plant, including marijuana and hashish. THC is the substance that affects the brain and causes changes in behavior and feelings. Hashish is the strongest of all substances made from cannabis. Hashish can be smoked and is also often taken by...