Before the 1960s, many Americans had never heard of marijuana, but today it is the most often used illegal drug in this country.
Cannabis is a term that refers to marijuana and other drugs made from the same plant.
They also contain more than 400 other chemicals. THC potency has increased since the 1970s but has been about the same since the mid-1980s. The strength of the drug is measured by the average amount of THC in test samples confiscated by law enforcement agencies. Hash oil, a tar-like liquid distilled from hashish, has an average of 16 percent, with a range as high as 43 percent.