Often, the effect of a drug gradually diminishes when it is given continuously or repeatedly. Desensitization and tachyphylaxis are synonymous terms used to describe this phenomenon, which often develops in the course of a few minutes. The term tolerance is conventionally used to describe a more gradual decrease in responsiveness of the drug, taking days or weeks to develop, but the distinction is not a sharp one.I also found this interesting, having experienced it myself:
It is a common experience that many side effects of drugs, such as nausea or sleepiness, tend to subside even though drug administration is continued. We may assume that some kind of physiological adaptation is occurring, presumably associated with altered gene expression resulting in changes in the levels of various regulatory molecules, but little is known about the mechanisms involved.It's amazing to me that such commonplace occurrences in pharmacology are so poorly understand! So much of medicine is still a mystery.
And finally, this one sentence made me incredibly nostalgic for my days as a synthetic chemist and for biochemistry: "It is no exaggeration to say that the ability of proteins to interact in a highly selective way with other molecules-- including other proteins-- is the basis of living machines."
