تسجيل الدخول

تسجيل

Tolerance

المؤلف:  Max M. Houck، Jay A. Siegel

المصدر:  Fundamentals of Forensic Science

الجزء والصفحة:  p359-360

2026-08-11

14

Tolerance

Chemical tolerance is a phenomenon whereby the body’s organ systems adapt to the drug. Then it takes ever-increasing doses to achieve an equivalent psychoactive effect. Most drugs will eventually exhibit tolerance to one degree or another, but it is more pronounced in some types, including opium-based narcotics such as morphine and heroin, as well as cocaine and barbiturates. The cause of tolerance appears to be a decrease in sensitivity or number of receptors for the drug. It usually takes many repeated doses of the drug over an extended period of time for tolerance to be manifested. If the drug is stopped, it may take a long time period for the body to recover. In some cases of extreme tolerance build-up, sudden withdrawal of the drug can be fatal. This has been demonstrated with barbiturate addiction. In the case of marihuana, there seems to be a sort of “reverse tolerance” taking place. Some users report that they don’t need to take more and more marihuana to achieve the same effects and, in some cases, they can decrease the dosage. The reasons for this are not well understood. It may be that the reactions that a person has to taking marihuana may be partly learned behavior and it takes time to learn to expect certain reactions. Another reason may be that marihuana may collect and persist in the body for a very long time—perhaps months, and the build-up of its psychoactive components may be the cause of the reverse tolerance. In the case of LSD, there is no evidence of drug tolerance but there is evidence that the drug may persist in the body for months or even years. Some regular users have experienced so-called “flashbacks.” This is an instance where the person experiences hallucinations months or years after the drug was last taken. This is all the more surprising since the dose of LSD that can cause hallucinations is about 50 µg, a very small amount by drug standards.