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How does receptor down-regulation contribute to drug tolerance?

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Receptor down-regulation is a biological process that contributes to drug tolerance—the phenomenon where an increased dose of a drug is required to achieve the same physiological effect over time.1

When a drug is administered repeatedly or over a prolonged period, the body often initiates adaptive responses to maintain homeostasis. One such mechanism is down-regulation, which involves the physical removal of receptors from the cell membrane following sustained exposure to an agonist.1

Because the number of available receptors on the cell surface decreases, the cell becomes less sensitive to the drug. Consequently, the drug’s ability to initiate its typical physiological or biochemical changes is diminished, necessitating higher concentrations of the substance to produce the original response. This process is a key component of desensitization, and while it is a reversible process, the recovery of receptor levels can take hours or even days after the drug is no longer present.1