A controlled substance is generally a drug or chemical whose manufacture, possession or use is regulated by a government and whose general availability is restricted. Controlled substances are substances that are the subject of legislative control. They may include prescription medications and drugs or other substances, which are strictly regulated or outlawed, because of their potential for abuse or addiction.
Most people take medicines only for the reasons their doctors prescribe them. But an estimated 20 percent of people in the United States have used prescription drugs for non-medical reasons. This is prescription drug abuse and it is a serious problem.