A therapist has a duty of care and that includes raising concerns about a client being possibly over medicated or showing side effects. That is not 'prescribing' anything, it's just good practice. They can also have just as much knowledge, and often more, about psychological conditions as a psychiatrist, particularly since psychiatry is so much dominated by a medical model. I would be more concerned if a therapist did not question things like that and just blindly went along with working with a client when they had concerns about their treatment or diagnosis.