Which of the following is an example of an antagonistic drug effect?

The correct answer illustrates an antagonistic drug effect where one drug counteracts the effects of another. In the case of cocaine and heroin, these two substances have opposing actions in the body. Cocaine is a stimulant that increases heart rate and energy levels, while heroin is an opioid depressant that slows down heart rate and induces sedation. When taken together, the stimulant effects of cocaine can mask the depressant effects of heroin, which could lead to dangerous outcomes, including respiratory depression or overdose, as users may not feel the full effects of the heroin.

The other options do not definitively represent antagonistic effects. Cocaine and cannabis generally produce differing effects but do not directly oppose one another. Heroin and methamphetamine can have overlapping effects since both can cause intense euphoria, though through different mechanisms. Alcohol and caffeine are also in this latter category, as caffeine can somewhat counteract the sedative effects of alcohol but does not truly negate them in the same way cocaine does with heroin. Understanding these interactions is crucial for recognizing the risks associated with poly-drug use in a law enforcement context.