Which finding would indicate to the nurse that a client is experiencing an adverse reaction to a new medication?

Shortness of breath is a significant finding that may indicate an adverse reaction to a new medication. This symptom can arise from various pharmacological effects, such as medications that may cause respiratory depression, allergic reactions, or exacerbation of underlying respiratory conditions. If a client experiences shortness of breath after starting a new medication, it is crucial for the nurse to assess the situation further and notify the healthcare provider, as this could be a sign of a serious and potentially life-threatening reaction.

In contrast, increased energy levels or improved sleep may be positive effects, indicating that the medication is working as intended, particularly if the drug is intended to enhance mood or treat a sleep disorder. Weight gain might be a side effect of some medications; however, it is not as immediately concerning as shortness of breath within the context of medication reactions.