Final answer:
The nurse should inform the client that combining St. John's Wort with fluoxetine can cause serotonin syndrome, as both increase serotonin levels in the brain and can lead to potentially serious side effects.
Step-by-step explanation:
The nurse should advise the client against taking St. John's Wort with fluoxetine. This combination can lead to serotonin syndrome, a potentially life-threatening condition characterized by excessive serotonin activity in the nervous system. Symptoms can include agitation, confusion, rapid heart rate, dilated pupils, loss of muscle coordination, and increased body temperature. Fluoxetine, as a selective serotonin reuptake inhibitor (SSRI), increases serotonin levels by preventing its reuptake in the brain. St. John's Wort also affects serotonin levels, and when taken together with an SSRI like fluoxetine, the risk of serotonin syndrome is heightened. The nurse should educate the client that herbal supplements like St. John's Wort can have interactions with prescription medications and it's essential to consult a healthcare provider before combining them.