Tolerance and Physical Dependence

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Tolerance and Physical Dependence

People who begin taking drugs often do so to achieve a certain effect that they find enjoyable or positive in some way. Prescription medications may be taken initially to treat pain, depression , or anxiety. Improper use of prescription and other drugs (including alcohol) may make a person feel alert, powerful, confident, relaxed, friendly, sexy, or talkative. These rewarding consequences increase the likelihood that a person will continue using a drug. Furthermore, two other important consequences that influence continued drug use are tolerance and physical dependence.

Physical dependence occurs when a person's body becomes accustomed to and dependent on the presence of a particular drug. When the dose is lowered or the drug is stopped, the person will begin to notice withdrawal symptoms. Resuming use of the drug eliminates the withdrawal symptoms. Some withdrawal symptoms feel like a flu bug. The individual may feel hot and sweaty, chilly and shaky. They may develop a runny nose and eyes, and itchy skin. Diarrhea and anxiety may also occur.

Physical dependence is not the same as addiction. Physical dependence is a totally biological response of the body; addiction includes psychological or behavioral factors. A person can be physically dependent on a drug but not addicted to it. For example, a patient who has been in the hospital after major surgery may be put on regular doses of narcotic painkillers. When these are stopped, he or she may notice symptoms of withdrawal. This person has become physically dependent on (but not addicted to) painkillers.

When drug users become tolerant to a drug's effects, they must increase the dose to feel the same effects of the original dose. An individual being treated for severe pain may develop tolerance to a prescription

Craving    XX
Sweating, feverX   X 
Nausea or vomitingX   X 
Malaise, fatigueXX X  
Hyperactivity, restlessnessXXXX X
InsomniaXXX X 
IrritabilityXX X X
AnxietyX XX X
DepressionX  X  
Difficulty concentrating     X
Gastrointestinal disturbance  X   
Increased appetite     X
Diarrhea    X 

painkiller. The health-care provider may need to increase the dose in order to appropriately treat the patient's pain.

A person who has several alcoholic drinks a night may find that he or she has to drink increasing quantities to achieve the effects obtained from the original amount. An alcoholic can appear normal at blood alcohol concentrations (BACs) that would make a social drinker pass out. That person's body has developed tolerance to alcohol's effects.

Tolerance can cause a person to take more of a certain drug regardless of the initial reasons for drug use. For example, a person may regularly drink alcohol to feel comfortable in social situations. If that person becomes able to drink large amounts of alcohol without getting sleepy or dizzy, his capacity to drink increases regardless of the reasons for his drinking.

A drug abuser who has become tolerant to a drug's effects may increase the dose of drug. But high doses often produce unwanted effects, such as dysphoria (a feeling of uneasiness) or physical illness. Once the user experiences these negative effects, he or she may stop using the drug. However, the drug abuser may also become tolerant to the drug's negative effects, and so continue drug use. In general, tolerance and physical dependence make stopping a drug very difficult.

Addiction is a condition that occurs due to both physical and psychological factors. The individual's body becomes physically dependent, and he or she develops tolerance to the drug's effects. However, a person who is addicted to drugs also develops psychological dependence on the drug. Drug use may cause multiple problems for an individual: in school, on the job, in personal relationships, in finances, and in health. Yet a person who is addicted to drugs overrides these negative consequences of drug use, and continues to seek out and use drugs. This person is truly addicted. Researchers would like to better understand how issues of physical dependence, tolerance, and addiction interact to make drug use such a hideous snare.

see also Addiction: Concepts and Definitions; Alcohol: Withdrawal; Benzodiazepine Withdrawal; Cocaine: Withdrawal; Nicotine Withdrawal; Nonabused Drugs Withdrawal.


If addicts can be punished for their addiction, then the insane can also be punished for their insanity. Each has a disease and each must be treated as a sick person.

William O. Douglas (1898 1980), U.S. Supreme Court Justice in Robinson v. California, 1962.