What type of drug can reverse the effect of another drug?

The correct answer is an antagonist. An antagonist is a type of drug that binds to a receptor in the body but does not activate it, effectively blocking the action of another substance—often a natural ligand or a medication that would normally activate that receptor. This blocking action can reverse or inhibit the effects of other drugs that act as agonists at the same receptor sites.

For example, in the case of opioid drugs, the antagonist naloxone is administered to reverse the effects of an opioid overdose. Naloxone competes for binding at opioid receptors and knocks the opioid out of its place, reversing its depressant effects on the central nervous system.

In contrast, analgesics are used primarily for pain relief, agonists actively promote a biological response, and stimulants generally increase activity in the nervous system. None of these categories inherently possess the property of reversing another drug's effects as antagonists do.