What Does Medication Tolerance Mean?


Medication tolerance, or drug tolerance, occurs when your body gets used to a medication so that either more medication is needed to give you the desired effect or a different medication is needed. Depending on the drug, tolerance can develop in several days or happen more gradually during a number of weeks.

Tolerance can have a positive result such as a reduction in unpleasant adverse effects due to the medication. However, as your body becomes tolerant to the medication, the medication becomes less effective.​

Specifics of Tolerance

Tolerance can be characterized as follows:

  • Reduced response to the same concentration of drug (pharmacodynamic or functional tolerance)
  • Increased clearance of the drug by liver metabolism (in other words, the drug is broken down and cleared from your body more easily)
  • Getting used to the drug effect (behavior or learned tolerance)

Examples of Medication Tolerance

Medication tolerance is most often related to drugs that affect your body’s brain and nervous system including:

  • Painkillers such as Oxycontin (oxycodone)
  • Tranquilizers such as Valium (Diazepam)
  • Over-the-counter sleep aids such as Benadryl (diphenhydramine)

Tolerance and Substances of Misuse

When a person first consumes a potential substance of misuse, be it alcohol, opioids or nicotine, the effects are more potent than they ever will be again. On repeated administration of this drug, a person needs larger and larger amounts to feel any desired effects thus setting up a vicious cycle of abuse, dependence, and withdrawal.  The phenomenon of needing more drug to produce the desired effect is called tolerance. 

Tolerance is a normal adaptive response to ingested drugs. Over time, your body changes with increased exposure to a drug. These changes occur at both a cellular level and affect the way that organs interact with each other.

When a person becomes tolerant of a certain CNS depressant like alcohol, then this person usually becomes tolerant of other drugs of misuse like heroin. (Technically, opioids like heroin aren't CNS depressants although they have depressant properties.) This phenomenon is called cross-tolerance.

Tolerance can be particularly dangerous because it hastens dose-dependent repercussions of drug use.

Certain people exhibit a rapid acute tolerance or initial tolerance to a drug. These people may be at higher risk of drug dependence or substance misuse.

If you feel that you may be experiencing tolerance to any substance of misuse, it's extremely important to inform your physician and get help. Substance misuse and drug dependence can not only have terrible and deadly personal consequences but consequences for your loved ones as well as society as a whole. Please remember that there are health care professionals and support groups who specialize in drug treatment and are empathetic to your needs. Here's a link to SAMHSA, the Behavioral Health Treatment Services Locator hosted by the U.S. government.

Content edited by Naveed Saleh, MD, MS, on 1/31/2016

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  • Martin PR. Chapter 15. Substance-Related Disorders. In: Ebert MH, Loosen PT, Nurcombe B, Leckman JF. eds. CURRENT Diagnosis & Treatment: Psychiatry, 2e. New York, NY: McGraw-Hill; 2008.