What is a known side effect of codeine?

Respiratory depression is a well-documented side effect of codeine, a medication classified as an opioid analgesic. Opioids like codeine work by binding to specific receptors in the brain and spinal cord, which can lead to significant decreases in respiratory rate and depth. This effect can be especially dangerous in situations of overdose or when used in combination with other central nervous system depressants, such as benzodiazepines or alcohol.

In contrast, the other options do not correlate with known side effects of codeine. Weight gain is not typically associated with opioid use; increased energy levels conflict with the sedative properties of opioids, which generally cause drowsiness; and while vision changes may occur due to various medications or conditions, they are not a common side effect of codeine specifically. Understanding these side effects is crucial for safe medication management and patient care.