Which of the following is a sign of opioid use?

Drowsiness is a well-documented sign of opioid use. Opioids are substances that can depress the central nervous system, leading to sedation and lethargy. This drowsiness can vary in intensity, depending on the specific opioid and the dose consumed. In the context of opioid use, this effect is significant because it can impair an individual's ability to perform tasks that require alertness and can therefore lead to dangerous situations, such as driving.

In contrast, the other options suggest effects that are not typically associated with opioid use. Increased energy and heightened alertness are more commonly linked to stimulants rather than opioids, which are known for their calming and pain-relieving properties. Intense euphoria is possible with opioids due to their action on the brain's reward pathways; however, it is not as direct a sign as drowsiness, which is more consistently observed among individuals using opioids. Therefore, drowsiness remains the most reliable indicator of opioid use in this context.