Early in the Christian Era it was grown in the Mediterranean countries of Europe, and its cultivation spread throughout the rest of Europe during the Middle Ages. Today the production of hemp for its fiber is a leading industry in India, Romania, China, Hungary, Poland, and Turkey. It is also grown in North and South America. The plant is an annual herb with angular, rough stems and alternate deeply lobed leaves. The plant's slender woody stalks are hollow except at the tip and base.
Hemp fibers come from the inner bark of the stalks.
After the stalks are cut, they must ret, or rot, so that the outer bark can be more easily removed. They are either soaked in pools in a process called water retting or left on the ground to absorb rain and dew, which is called dew retting. The stalks are then dried and crushed. A shaking process completes the separation of the fiber from the woody portion. The active ingredient in these drugs is present in all parts of both the male and female plants but is most concentrated in the resin in the flowering tops of the female.