What physical sign may indicate a head injury in a patient using opioids?

Miosis, or constricted pupils, is a well-known effect of opioid use and can also be an indicator of central nervous system (CNS) disturbances, including potential head injuries. In patients using opioids, miosis can signify that the opioid is affecting the body’s response to pain and may also correlate with altered neurological status.

In the context of a head injury, miosis may suggest increased intracranial pressure or changes in the brain's function due to trauma. This link between pupil size and neurological conditions highlights the importance of monitoring changes in pupil diameter when assessing a patient who has sustained a head injury, especially one who is being treated with opioids.

Other options do not relate directly to head injuries or are not clearly associated with opioids. Flushing of the skin, for instance, does not indicate a head injury and might suggest a different etiology such as an allergic reaction. Increased appetite and weight gain are typically associated with several other conditions and not commonly linked to acute assessments of head injury or the effects of opioids. Thus, miosis stands out as the most significant physical sign in this context.