Controlled substances are drugs or chemicals that are regulated by law due to their potential for abuse or addiction. These substances are classified into different schedules based on their medical use, safety, and potential for dependency. For example, Schedule I substances, like heroin and LSD, have no accepted medical use and a high potential for abuse. The regulation of controlled substances is managed by agencies such as the Drug Enforcement Administration (DEA) in the United States. This ensures that these substances are prescribed, dispensed, and used safely, minimizing the risk of misuse and protecting public health.