A nurse is caring for a client with bipolar disorder who is prescribed fluoxetine, an SSRI. The client has recently started taking St. John's wort on a friend's recommendation. Which nursing action is the priority to prevent a serious adverse effect?

A. Instruct the client to immediately discontinue St. John's wort and notify the provider due to risk of serotonin syndrome: St. John's wort can increase serotonin levels and, when combined with an SSRI like fluoxetine, significantly raises the risk of serotonin syndrome. Prompt discontinuation and provider notification are critical to prevent this potentially life-threatening adverse effect. B. Encourage the client to increase fluid intake to prevent dehydration from diarrhea: While hydration is important, it does not address the primary risk of serotonin syndrome, which requires immediate intervention rather than supportive measures. C. Advise the client to continue St. John's wort but monitor for mild gastrointestinal side effects: Serotonin syndrome can present with symptoms such as agitation, confusion, rapid heart rate, and hyperthermia. Monitoring for minor GI effects ignores the life-threatening risk. D. Suggest the client reduce the dose of fluoxetine while taking St. John's wort to minimize serotonin effects: Self-adjusting SSRI doses is unsafe and may lead to subtherapeutic treatment or increased adverse effects. Dose changes must be guided by a healthcare provider, not the patient.