Drug overdose occurs when a person takes more than the medically recommended dose of a prescription or over-the-counter drug. Overdose may result when a young child or an adult with impaired mental abilities accidentally ingest a medication left within their reach. An adult, especially seniors or people taking multiple medications, can mistakenly ingest the incorrect medication or take the wrong dose of a medication. Some individuals may also be hyperreactive to a medication and even a therapeutic dose may be toxic.