Drug tolerance happens when a drug becomes less effective.Share on Pinterest

There’s a lot of confusion around words like “tolerance,” “dependence,” and “addiction.” Sometimes people use them interchangeably. However, they have very different definitions.

Let’s look at what they mean.

Tolerance is common. It can develop when your body is regularly exposed to a medication.

If your body has developed a tolerance to a medication you’re taking, it means the medication at your current dose has stopped working as effectively as it once did.

It might mean your body becomes used to the medication, and you don’t get the same benefits or effects as before. Your doctor may need to increase the dose, change the regimen, or in some cases, prescribe a different medication.

There are genetic and behavioral elements involved with tolerance. Sometimes tolerance can develop quickly, even the first few times you take a medication.

Tolerance isn’t the same as dependence.

Important Facts About Tolerance
  • Tolerance is still not well understood. Researchers are still looking at why, when, and how it develops in some people and not others.
  • It can happen with any drug, including prescription and unregulated drugs, like cocaine.
  • Your condition might worsen because the medication isn’t working as well.
  • Cross-tolerance could occur. This is tolerance to other drugs in the same class.
  • With certain classes of drugs, like opioids, tolerance can increase the risk of dependence, addiction, and overdose.
  • When your body develops tolerance, using higher doses increases the risk of overdose.
  • A benefit of tolerance might be fewer side effects as your body gets used to the medication.

The difference between tolerance and dependence has to do with how the body reacts to the presence or absence of a specific drug.

With tolerance, certain cell receptors in the body that activate when the drug is present stop responding like they once did. Your body might clear the medication faster, too. Scientists still don’t fully understand exactly why this happens in some people.

With dependence, if the drug isn’t present or the dose is suddenly reduced, you might experience withdrawal. This means the body can only function normally when the drug is present. It can happen with many drugs. In some cases, dependence can lead to addiction.

Withdrawal symptoms will depend on which drug you’ve been using. They can be mild, like nausea or vomiting, or more serious, like psychosis or seizures.

If your body is dependent on a drug, it’s important to not abruptly stop taking it. Your doctor will put you on a schedule to gradually ease off the drug to avoid withdrawal symptoms. They can also recommend resources to support you.

Tolerance and dependence are different from addiction. This is a more serious condition.

Addiction is more than drug dependence. It’s a health condition like any other chronic condition. It involves changes in brain activity: Neurotransmitters like dopamine are repeatedly triggered and increase drug cravings.

Addiction is also referred to as substance use disorder.

Addiction is a driving need to use a drug despite the potential for harm, like compromising work, social, and family needs. A person with a substance use disorder will experience a cycle of stress and anxiety around getting the drug.

Whether someone develops addiction depends on genetic factors (including family history of addiction) as well as social and environmental factors. It’s not an intentional choice.

Drug tolerance can be a challenge in the treatment of certain conditions, including:

  • chronic pain
  • immune-related conditions
  • seizure disorders
  • some mental health conditions

When tolerance develops, doctors have to find new ways to effectively manage symptoms.

risks of drug tolerance

Risks from developing tolerance can include:

  • Relapse or flare-up of a condition. The medication may become not as effective, like with antipsychotics and anti-seizure drugs.
  • Need for higher doses. More of the drug is needed to achieve symptom relief, which may increase negative side effects of the drug.
  • Addiction. For example, higher doses of opioids can increase the risk of developing a substance use disorder in some people.
  • Unintentional medication errors. This may occur from changes to dosing or regimen.
  • Cross-tolerance. For instance, in certain cases, alcohol can cause cross-tolerance to other drugs, like diazepam or valium.

As mentioned, tolerance can develop to many classes of medications and is a normal reaction. Your doctor will carefully monitor you to manage the effects of tolerance.

In some cases, your doctor might slowly stop the medication and restart it after a break, depending on the condition. This gives your body a chance to reset. It doesn’t always work long term but can be one option to try.

examples of drug tolerance

Some medications and conditions with reports of tolerance include:

  • Anti-depressants. Depression symptoms can worsen in some people.
  • Antibiotics. They can have weaker effects. This is different from drug-resistance.
  • Anxiolytics. Your body may develop tolerance and dependence. Anticonvulsant and other effects of benzodiazepines, a type of anxiolytic, aren’t well understood. GABAA receptors may play a role.
  • Cancer. Multi-drug tolerance can develop after initial success in the treatment of different cancers. A “drug holiday” can sometimes reset effectiveness.

With certain medications, developing tolerance means your doctor will need to reevaluate your treatment.

This can be challenging sometimes, because increasing the dose might mean more side effects. It might be harder to find other medications that work. For other, unregulated drugs, there are more risks of overdose and other complications.

Tolerance can happen if you’ve been using a medication or other drug for a while. If you think your body has developed drug tolerance, talk to your doctor.

Don’t suddenly stop taking the drug. There are steps your doctor can take to manage drug tolerance and help you feel better.