Question

tolerance to opioids, which occurs due to a decrease in the number and sensitivity of opioid receptors to opioids, means that users must __________. take larger and larger doses cut back dramatically on their dose (=reduce their doses a lot) continue taking the same dose

Explanation:

Tolerance to opioids means the body needs more of the drug to achieve the same effect as the number and sensitivity of opioid - receptors decrease. So users must take larger doses.

Answer:

take larger and larger doses