That's not correct. Not all prescription medications are controlled substances. Controlled substances are a subset of prescription medications that have a high potential for abuse, such as narcotics, for example. They are specified in the Controlled Substances Act, and are regulated by the DEA. Controlled substances have much tighter controls placed on their prescriptions than other prescription drugs, such as limits on the number of pills that can be prescribed at one time, the number of refills permitted, requiring the use of special prescription forms, etc. In addition, prescriptions written for controlled substances are monitored, and prescribers can face investigation if they appear to be over prescribing them.