Can a drug tolerance cause a drug overdose?

Drug tolerance can increase the likelihood of drug overdose for several reasons: 1) A person addicted to a drug to which they've built tolerance may overestimate the amount of the drug they need to ingest to get high. For instance, a heroin addict might find they need more and more heroin to stay "well" as the months go by. They might assume that they can put off the effects of withdrawal by doing double the amount of heroin they did yesterday. This can lead to an overdose. 2) The other reason tolerance can contribute to overdose is if someone who has had a period of sobriety thinks they can use the same amount of a drug that they used before their sobriety. This is a very common cause of death amongst heroin users. Alcohol is one of the only drugs in which tolerance can lead to death, without the overdose. When a person becomes physically addicted to alcohol (usually will experience delirium tremens when they have had short periods of time without alcohol), they can die when they try to quit drinking. Often the alcoholic will have seizures and needs prompt medical attention to prevent death.