Depressants are substances that depress the activity of the central nervous system. Depressants are often referred to as "downers" because of their sedative, hypnotic and tranquilizing effects. There are both legal and illegal depressants. Alcohol is the most common legal depressant. Other depressants that are legal are often prescribed medications used to induce sleep, relieve stress, and subdue anxiety. These prescriptions are often abused as well, such as the case with rohypnol. GHB is an illegal depressant often used in drug-facilitated sexual assaults because of its sedative properties.