Some prescription drugs create a dependency quickly in the body by altering chemicals in the brain (this can happen even when taken as prescribed). In these cases, the drug is usually prescribed as a short-term solution. If a person continues to take this medication, an addiction may develop.
Other prescription drugs create a sense of euphoria when taken, which may encourage people to take the medication more often or in larger doses than prescribed. When this happens a tolerance can develop, and eventually, physical or mental addiction to the substance occurs.