Tolerance, Physical Dependence, and Addiction Explained

Medically Reviewed by Smitha Bhandari, MD on April 21, 2022
6 min read

The words “addiction,” “tolerance,” and “physical dependence” are often used interchangeably when it comes to drug or alcohol use. But they don’t mean the same thing. The words we use can affect how we feel about ourselves. They can also affect how we get help from health care providers. So what is the difference between addiction, tolerance, and physical dependence?

Addiction is a long-term brain disease. When addiction is related to drugs or alcohol, the condition is also called a substance use disorder. Addiction has no cure, but it can be managed with treatment. “Drugs,” in this case, means any substance that affects the body. It could include prescription drugs, over-the-counter products, street drugs, alcohol, even nicotine.

The National Center for Drug Abuse Statistics says more than 20 million people over the age of 12 in the United States have substance use disorder. Most commonly, the cases are related to marijuana and prescription pain relievers. Addiction is considered “highly treatable.” But it can take a few tries for the therapy to be fully effective. And the disease has a 40-60 percent relapse rate.

People who are addicted to a substance use it even if it has no medical benefit. They use the substance no matter what and despite the consequences. Addictions are more likely to result in serious harm, including suicide, unlike tolerance and physical dependence.

Many drugs can cause addiction, but the addictive drugs used most often include:

  • Marijuana (cannabis)
  • Prescription and nonprescription opioids like fentanyl and heroin
  • Stimulants like methylphenidate (Concerta, Ritalin)
  • Sedatives or tranquilizers called central nervous system (CNS) depressants, like alprazolam (Xanax), phenobarbital, and zolpidem (Ambien)
  • Dextromethorphan, found in over-the-counter cough suppressants


If you develop a tolerance to a substance, it becomes less effective for you. For example, if you take a sedative to sleep, it may work very well at the first dose. But over time, you can develop a tolerance. That means you need a higher dose to get the same results. The same thing happens with alcohol. When you first start drinking alcohol, it may have taken only a few drinks for you to feel drunk. But over time, you may need more drinks, more often, for the same effect.

Becoming tolerant to a drug isn’t unusual, especially if you take it for a long time. Tolerance can lead to addiction in some people, but it is not the same thing as addiction. Being drug-tolerant doesn’t necessarily mean you will become addicted. But it could be a warning sign for you to be careful.

Speak with your doctor if you develop a tolerance to your medication or any other substance. If you are taking a prescription medication, your doctor may change the class of medication, which may affect your body in a different way. If it is not a prescription medication, your doctor may be able to help you reduce your use of the substance with the least side effects.

Physical dependence

Physical dependence on a drug is also different from addiction. But physical dependence can lead to addiction.

Unlike tolerance, which focuses on how much of the substance you need to feel its effect, physical dependence happens when your body starts to rely on the drug. If you were to suddenly stop using it, you would likely experience some harsh symptoms.

Caffeine is an example of a common substance that causes physical dependence. If you can’t function properly in the morning without your cup of coffee, it could be that you are caffeine-dependent. When you miss your morning cup, you might develop physical withdrawal symptoms, like a headache, fatigue, difficulty concentrating, and more.

Other common substances that cause dependence are nicotine and pain relievers, particularly narcotics. Stopping suddenly will likely cause symptoms, and they can be serious. So unless it is urgent, gradually cutting down on the amount and how often you use it should make it easier. If you were addicted to the substance, just cutting down wouldn’t ordinarily work. The symptoms and cravings would be too strong to fight.

Speak with your doctor if you have become physically dependent on a medication or other substance. Together, you can plan on how to reduce your dependence.

The crossover from tolerance or dependence to addiction may not be obvious at first, but there are definite signs. These include (but are not limited to):

  • You take prescription medications, such as pain relievers or anxiety medications, when you don’t need them anymore.
  • You need higher doses more often to get the same effects.
  • You think about taking the drugs constantly and make sure you know where you can get more and how to get more.
  • You hide the fact that you are taking the drug or its effect on you.
  • You lie and steal to help you get the drug.
  • You take dangerous risks, like driving under the influence.
  • You can’t skip a dose without serious withdrawal symptoms.
  • You lose interest in things you used to enjoy.
  • You have trouble going to and staying at work or school.

Anyone can have an addiction, but some people are at higher risk. The most common risk factors for addiction include:

  • Genetics. Addiction can run in families, particularly if it is your sibling or parent who has it.
  • Depression, attention deficit hyperactivity disorder (ADHD), or posttraumatic disorder (PTSD). These and other mental health issues can cause someone to use substances to help them deal with their condition.
  • Early use. People who start to use drugs when they are young, while their brain is still forming, can become addicted more easily.
  • Using drugs that are highly addictive. Drugs such as cocaine, opioids, and stimulants can cause addiction faster.
  • Peer pressure. As young people try to fit into social groups, they may feel pressured to try addictive drugs.
  • Difficult family environment. Children who are not supervised may find themselves taking drugs to either fit in with their peers or to deal with negative feelings.

People used to believe that addiction only happened in certain areas, like in inner cities, or among specific groups of people, like those who were down and  out. But addictions can happen anywhere, from college campuses to rural and suburban towns. And anyone can become addicted, from people experiencing homelessness to business executives. Addictions can start slowly as people experiment with different types of drugs. Or they can come on quickly, like what is now happening in the opioid crisis. The opioid crisis is so bad that the U.S. government declared a public health emergency.

There are also myths about when you go for help. For example, we have long been told that people need to hit “rock bottom” before they’ll get help, but this isn’t true. Anyone with an addiction can get help at any point if they feel it’s the right time. And there are many ways that people can get help. Rehab is not the only solution.

Finally, there’s the myth that if you relapse after beating your addiction, you have failed. Just like with other diseases, sometimes you need multiple treatments or repeat treatments. Going through a relapse does not mean you’ve failed. It just means that you need more help.

If you believe you have an addiction, it’s never too late to look for help. It is treatable. Speak with your doctor or contact a substance abuse clinic. Working with a health care professional will allow you to explore the options to treat your addiction.

There is no one-size-fits-all path to addiction treatment. Some people do well at home with regular doctor visits and support groups. Some people need to stay in a rehabilitation facility. And sometimes it takes more than one type of treatment to be successful. The important thing is not to give up.