Marijuana is a drug made from the flowers, stems, seeds, and leaves of the hemp plant. It is usually smoked as a cigarette or in pipes like a bong (water pipe). 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 artificial chemicals resemble THC (synthetic cannabinoids), but are much stronger than THC. They are sometimes called spice or K2. To learn more about marijuana, take this quiz, based on information from the National Institute on Drug Abuse (NIDA).