A recreational drug and medicine derived from the leaves of the cannabis sativa plant. When inhaled, it makes the user feel relaxed and euphoric. The pharmacologically active ingredient in marijuana is tetra-hydro-cannabinol.

Regular marijuana use may cause red eyes, lethargy and uncoordinated body movements. The long-term effects may include decrease in motivation and other undesirable effects on the brain, heart, lung and reproductive system.

Studies have shown that smoking marijuana once a week or more apparently doesn't harm the lungs, unlike the damages done by tobacco.