Final answer:
Naltrexone can prevent heroin from having its normal effect if it is injected.
Step-by-step explanation:
The statement is true that the opioid antagonist naltrexone can prevent heroin from having its normal effect if it is injected.
Opioid antagonists are medications that block the effects of opioids by binding to opioid receptors without activating them. These drugs are used primarily to reverse the effects of opioid overdose, which can be life-threatening. Opioid antagonists can quickly and effectively counteract the respiratory depression, sedation, and other effects caused by opioid overdose.