The definition of drug tolerance is the 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 a human, animal, disease, or tissue fails to respond to the intended effectiveness of a chemical or drug.
Dexedrine is one such drug that many build a tolerance to. Many experience
tolerance, extreme psychological dependence, and severe social disability. There
are reports of patients who have increased the dosage to many times that recommended.
Abrupt cessation following prolonged high dosage administration results in extreme
fatigue and mental depression; changes are also noted on the sleep EEG. Manifestations
of chronic intoxication with amphetamines include severe dermatoses, marked
insomnia, irritability, hyperactivity, and personality changes. The most severe
manifestation of chronic intoxication is psychosis, often clinically indistinguishable
The way the brain responds to pleasure and pain could explain how people develop a tolerance for prescription drugs they're abusing such as Dexedrine. One problem seen in people who abuse prescription drugs is that they build up a tolerance for the drug, so it takes a bigger dose to get the same effect. Researchers at UT Southwestern Medical Center at Dallas have found an important clue to how this happens. In earlier research, these scientists found that drugs that are commonly abused activate a protein in the part of the brain that is responsible for reward and motivation processes.
Their new study found that both pain and pleasure cause changes in this part of the brain. These changes could explain how tolerance for a drug develops. Researchers studied mice in which the brain protein had been genetically activated, reproducing the effect of drugs on the brain. These mice were exposed to both pleasurable and painful stimuli and tested for their sensitivity to these stimuli. Their emotional response to stimuli decreased. Meanwhile, mice who had lower levels of the protein showed the opposite response.
Because the emotional response to both pleasure and pain was affected, Dr. Michael Barrot, the researcher who led the study, says that the same function in the brain that's affected by drug abuse may also play a role in emotional disorders like depression. Both drug abuse and depression may have similar biological causes, and understanding how these biological mechanisms work may help doctors prevent and treat both drug abuse and emotional disorders.