Drug tolerance occurs when a person no longer responds to the effects of a drug. When a person develops a drug tolerance they need a higher dose of the drug to achieve the same effect. When drugs are used repeatedly over time, a tolerance to them may develop. For example, when alcohol or a drug like heroin is used for long periods of time, higher doses must be taken to experience the effects.
Drug tolerance typically occurs because the metabolism of the drug speeds up. It also occurs due to the strength of the cell receptors that a drug attaches to becoming weaker. A person can become both physically and psychologically tolerant to a drug.
Physical tolerance occurs when the body increases the rate that the drug is broken down. The body can eventually adapt to the regular presence of the drug in the system. When this occurs, the body stops “listening” to what the drugs are trying to tell them.
Psychological tolerance occurs when a person becomes accustomed to the drug and stops feeling the effects. A person can also offset for the way the drug makes them feel, and feel and act as if they aren’t affected by the drug at all.
There are three types of drug tolerance.
Drug tolerance should not be confused with drug dependence. A person who has developed a tolerance to drugs or alcohol is not always dependent or addicted. Signs of drug tolerance include needing more of a medication or drug to achieve the desired effects. When a person with a drug tolerance is given a higher dosage, the effect of the drug can become improved. This however, can accelerate tolerance and reduce the effects of the drug. One of the biggest signs of a drug tolerance is the need for larger doses to feel the desired effects.
No. A person who has developed a tolerance to drugs is not necessarily dependent upon them. Dependence occurs when a person feels withdrawal symptoms when discontinuing the use of a drug.
Not necessarily. Addiction typically develops due to different environmental, personal, and biological factors that have affected a person’s life. Not everyone who has developed a tolerance to drugs or alcohol will develop an addiction.
It can be. A person who is at risk for addiction can develop a dependence upon a drug if higher dosages are prescribed, which is typical when a person develops a tolerance. A drug tolerance doesn’t reduce the risks of any side-effects from the drugs a person is taking. Taking a higher dosage may increase the severity of the side-effects a person experiences.
The Neurobiology of Drug Addiction, Definition of tolerance, DrugAbuse, 2007
Drug Abuse and Treatment FAQ, National Institute on Drug Abuse, 2017