Many people think drug addiction, dependence, and tolerance are pretty much the same thing. But in fact, each term means something very different about how drugs affect a person’s body and brain. Learning the difference is important.
Tolerance happens when a person no longer responds to a drug in the way they did at first. So it takes a higher dose of the drug to achieve the same effect as when the person first used it. This is why people with substance use disorders use more and more of a drug to get the “high” they seek.
Dependence means that when a person stops using a drug, their body goes through “withdrawal”: a group of physical and mental symptoms that can range from mild (if the drug is caffeine) to life-threatening (such as alcohol or opioids, including heroin and prescription pain relievers). Many people who take a prescription medicine every day over a long period of time can become dependent; when they go off the drug, they need to do it gradually, to avoid withdrawal discomfort. But people who are dependent on a drug or medicine aren’t necessarily addicted.
Unlike tolerance and dependence, addiction is a disease but like tolerance and dependence, addiction can result from taking drugs or alcohol repeatedly. If a person keeps using a drug and can’t stop, despite negative consequences from using the drug, they have an addiction (also called a severe substance use disorder). But again, a person can be dependent on a drug, or have a high tolerance to it, without being addicted to it.