A nurse is monitoring a client receiving baclofen (Lioresal) for side effects related to the medication. Which of the following would indicate that the client is experiencing a side effect?

Baclofen is a muscle relaxant commonly used to treat spasticity. One of the well-known side effects of baclofen is sedation or drowsiness. This occurs because baclofen acts on the central nervous system to inhibit motor nerve activity, which can lead to feelings of tiredness or sleepiness.

In the context of monitoring for side effects, drowsiness is a key indicator that the medication is affecting the client as intended, potentially leading to decreased alertness and other CNS-related effects. It's essential for healthcare providers to acknowledge and assess this side effect, as it can impact the client's safety, especially if they need to perform activities that require full attention.

Other symptoms listed, such as polyuria (excessive urination), diarrhea, and muscular excitability, are not typical side effects associated with baclofen. While they may indicate other medical issues or adverse reactions, drowsiness is a well-documented and expected side effect of the medication, making it the most relevant choice when identifying a reaction to baclofen in this context.