What is a controlled substance, and why do the rules around my ADHD prescription feel so different?

A controlled substance is a medicine that the law places in a stricter scheduling category because of misuse and diversion risk, not because a patient did something wrong. In Canada, stimulants such as methylphenidate and amphetamines used for ADHD are controlled under the Controlled Drugs and Substances Act framework. Prescriptions can have extra rules on refills, transfers, and identification compared with many non-controlled medicines. References: https://www.canada.ca/en/health-canada/services/health-concerns/controlled-substances-precursor-chemicals.html https://laws-lois.justice.gc.ca/eng/acts/c-38.8/ https://www.gov.uk/government/publications/controlled-drugs-list--2