There are three main forms of illicit cannabis: the dried leaves and flowers (heads) of the cannabis plant; hashish; and hash oil.  Hashish is made from the resin (a secreted gum) of the cannabis plant. It is extracted from the cannabis plant, dried and pressed into small blocks. Hash oil is a thick oil that is distilled from the cannabis plant or hashish. The dried leaf of the cannabis plant is the least potent form of cannabis, while hash oil is the most potent form.