Final answer:
Drug tolerance involves the downregulation of receptors, leading to decreased sensitivity to the drug and requiring higher doses to achieve the same effect.
Step-by-step explanation:
Drug tolerance occurs when a drug user requires more and more of a given drug in order to experience the same effects of the drug. This phenomenon is linked to physiological dependence and involves the mechanisms by which drugs exert their effects on brain chemistry. These mechanisms include the downregulation or upregulation of neurotransmitter receptors, which can decrease or increase sensitivity to the drug, and changes in neurotransmitter activity that can enhance, inhibit, or mimic the action of neurotransmitters.
Specifically, the correct answer to the student's question about the mechanisms that cause drug tolerance is: A) Downregulation of receptors; which leads to a Decrease in sensitivity to the drug. When receptors are downregulated, there are fewer receptors available for the drug to act upon, which means that a higher dose of the drug is required to achieve the same effect.