Why do people become addicted to medications?

Why do people become addicted to medications?

Most people who drink alcohol and use other over the counter or prescription drugs, such as pain killers, do so infrequently and/or at levels that do not pose a danger to themselves or others.  Although in the case of prescription medicine or over the counter medicine, there are always instructions for the novice user such as how best to use, when not to use the drug and signs to look out for that might indicate an acute problem