Drug tolerance

In physiology, physiological tolerance or drug tolerance is commonly encountered in pharmacology, when a subject's reaction to a drug (such as a opiate painkiller, benzodiazepine or other psychotropic drug) decreases so that larger doses are required to achieve the same effect. Drug tolerance can involve both psychological drug tolerance and physiological factors. Characteristics of drug tolerance: is reversible, rate depends on the particular drug, dosage and frequency of use, differential development occurs for different effects of the same drug. Physiological tolerance also occurs when an organism builds up a resistance to the effects of a substance after repeated exposure. This can occur with environmental substances such as salt or pesticides.
Tachyphylaxis is a medical term referring to the rapid decrease in response to a drug after repeated doses over a short period of time.

There are two major mechanisms for tolerance

* Dispositional tolerance: occurs because of a decreased quantity of the substance reaching the site it affects.
* Reduced responsiveness: the response to the substance is decreased by cellular mechanisms.

Health Tolerance

Progressive diminution of the susceptibility of a human or animal to the effects of a drug, resulting from its continued administration. It should be differentiated from drug resistance wherein an organism, disease, or tissue fails to respond to the intended effectiveness of a chemical or drug. It should also be differentiated from maximum tolerated dose and no-observed-adverse-effect level.

Medicine

A condition in which the body becomes accustomed to a drug so that the previous dose no longer produces the desired effects and a progressively larger dose is needed to achieve a previously observed effect. Source: European Union.

Specialty Definition of Drug tolerance

Psychological drug tolerance: The CREB protein, a transcription factor activated by cyclic adenosine monophosphate (cAMP) immediately after a high, triggers genes that produce proteins such as dynorphin, which cuts off dopamine release and temporarily inhibits the reward circuit. In chronic drug users, a sustained activation of CREB thus forces a larger dose to be taken to reach the same effect. In addition it leaves the user feeling generally depressed and dissatisfied, and unable to find pleasure in previously enjoyable activities, often leading to a return to the drug for an additional "fix"

In physiology, tolerance occurs when an organism builds up a resistance to the effects of a substance after repeated exposure. A drug that produces an effect may lose effect at higher or repeated dosages. See also desensitization; tachyphylaxis or tolerance in physiology.

Drug tolerance occurs when a subject's reaction to a drug (such as a painkiller or intoxicant) decreases so that larger doses are required to achieve the same effect. This can easily lead to overdoses, especially of illicit drugs.

Tolerance may be related to the familiarity of "drug onset cues". The body is conditioned to respond to environmental cues such as the sight of a needle, and actually produces the beginnings of physiological responses before the drug is introduced. If there is no actual drug that follows, or if the dose is too small to produce the expected effect, it can trigger intense cravings in the addict. This may explain why "just one drink", or even the sight or presence of familiar alcohol cues, can cause a relapse in a recovering alcoholic.

Tachyphylaxis is a medical term referring to the rapid development of drug tolerance.

In a different context, drug tolerance can refer to the lenient policies of a government or organization toward drugs that are considered illegal in other areas. For example, the distribution of marijuana has been legal in the Netherlands since the early 1970s, and the state of California continues to test the legality of its medical marijuana laws.

Drug intolerance is another social issue. Many law enforcement and civic agencies (such as schools and scouting groups) advocate a zero tolerance policy towards drugs, meaning that any infraction of existing laws and regulations will be punished, no matter how small.

Drug resistance

Drug resistance is the reduction in effectiveness of a drug in curing a disease or improving a patient's symptoms. When the drug is not intended to kill or inhibit a pathogen, then the term is equivalent to dosage failure or drug tolerance. More commonly, the term is used in the context of diseases caused by pathogens.

Pathogens are said to be drug-resistant when drugs meant to neutralize them have reduced effect. When an organism is resistant to more than one drug, it is said to be multidrug resistant.

Drug resistance is an example of evolution in microorganisms. Individuals that are not susceptible to the drug effects are capable of surviving drug treatment, and therefore have greater fitness than susceptible individuals. By the process of natural selection, drug resistant traits are selected for in subsequent offspring, resulting in a population that is drug resistant.

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