Prescription painkillers, drugs to treat sleep disorders, anti-anxiety drugs, and stimulants are powerful drugs. It is important to follow a doctor’s, health care provider’s, or pharmacist’s instructions about how much to take and what things to avoid. For example, taking more than the prescribed amount of any prescription drug can lead to an overdose. People who overdose may vomit or even fall into a coma, depending on the drug. In addition, a person may have serious side effects from mixing prescription drugs with other medicines, over-the-counter drugs, or alcohol.