Types of Tolerance

[pharmapsyche]

Repeated use of a drug usually enables the body to develope tolerance to it's effects. Tolerance occurs with all drugs, but it can occur slowly or rapidly, and last for a longer or shorter time, depending on the type of drug. Tolerance to opiates can take weeks or months to envole and then equally long to resolve, while tolerance to hallucinogens occurs within a day but is resolved within a week.
Tolerance to a drug takes place in several ways such as the following:

Dispositional Tolerance:
The body speeds up the metabolism of the drug in order to eliminate it. This is usually accomplished by an increase in the production of enzymes in the liver that break down the drug. One way of testing the burden of drugs in the body is by measuring these enzymes-if they are high, the body is suffering from the drug effects.

Pharmacologic Tolerance:
With repeated use, the brain's neurons become less sensitive to the effects of the drug and may even produce an antidote or antagonist to the drug. Most neurons react to the overwhelming presence of a neurotransmitter like drug by downgrading the receptors for it. With opioids, the brain can actually produce an opioid antagonist, cholecystoknin, to counteract it's effects. This type of tolerance is very frustrating to drug users, who require increasingly higher doses to achieve the same effect.

Behavioral Tolerance:
The brain learns to compensate for the effects of the drug by using parts of the brain that are not affected. This is how chronic alcohol and marijuana users manage to function quite well despite levels of intoxication that would incapacitate people who are less accustomed to the drug.

Reverse Tolerance:
A drug user may actually become more sensitive to a drug when that drug destorys brain tissue. The excessive sensitivity may alter the overall drug experience to make it less enjoyable. MDMA is an example of a drug that often becomes very disagreeable with extensive use.

Acute Tolerance:
Also known as tachyphylaxis, this is the almost immediate tolerance to the effect of a drug as the body adapts to it. For example, a single dose of most hallucinogens causes a reduced effect if the drug is taken again, and even if a different type of hallucinogen is taken. For LSD-25, Psilocybin, and other hallucinogens, it may take a week to regain full sensitivity to the drug.

Select Tolerance:
The body develops tolerance to different aspects of the drug at different rates. For example, mental tolerance may proceed rapidly, so that the user wants a higher dose, but if physical tolerance has not caught up the user may take a fatal overdose. This has often happened with barbiturates.

Inverse Tolerance:
Repeated use of some drugs can suddenly cause a increased sensitivity to it, as the brain antcipates and enhances its effects. For example, long-term marijuana or cocaine users often become more sensitive to the drug, and even a fake look-alike drug may give them the drug effect, this is known as the Placebo Effect.

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