Final answer:
Opioid antagonists decrease the activity of opioid neurotransmitter systems and block the effects of opioid drugs.
Step-by-step explanation:
Opioid antagonists are drugs that decrease the activity of opioid neurotransmitter systems in the body. They work by blocking or impeding the normal activity of opioid receptors, which are responsible for reducing pain and producing euphoria. By blocking these receptors, opioid antagonists can reverse the effects of opioid drugs, such as analgesia and respiratory depression. Examples of opioid antagonists include naloxone and naltrexone.