Which of the following is NOT considered an adverse effect of opioid analgesics?

Opioid analgesics are known for their various side effects due to their mechanism of action in the central nervous system. While nausea, respiratory depression, and constipation are all established adverse effects related to opioid use, skin rash is relatively uncommon and not typically classified among the primary adverse effects of these medications.

Nausea can occur due to the effects of opioids on the central nervous system and gastrointestinal tract. Respiratory depression is a significant concern with opioids, as they can depress the respiratory drive, potentially leading to serious complications. Constipation is also a well-known effect, as opioids slow gastrointestinal motility.

In contrast, while some individuals may experience allergic reactions or rashes from any medication, including opioids, skin rash is not a predictable or common adverse effect that is regularly associated with opioid therapy. This distinction makes skin rash the correct answer, as it does not fit within the expected adverse effects relevant to opioid analgesics.