Knowing about marijuana can help you recognize its use in others, so you can encourage them to seek treatment. Marijuana is a street drug made from the flowers, stems, seeds, and leaves of the hemp plant. It is usually smoked as a cigarette, in a pipe, or in a cigar casing in which the inner tobacco has been replaced with marijuana. Marijuana also can be consumed by mixing with foods, brewing into a tea or "vaping" in an e-cigarette device. The main active ingredient is a chemical called THC (tetrahydrocannabinol). Some man-made chemicals resemble THC (synthetic cannabinoids), but are much stronger than THC. They are sometimes called "spice." To learn more about marijuana, take this quiz, based on information from the National Institute on Drug Abuse (NIDA).