Psychiatrymiddle twist
A 45-year-old man with major depressive disorder has been treated for seven weeks and his mood has clearly improved. He now reports intensely vivid, unpleasant dreams from which he wakes in the early hours. His wife says his legs jerk repeatedly, every twenty to forty seconds, for much of the night, and she is being woken by it. He does not snore and has no sleep attacks by day. Ferritin, renal function and thyroid function are normal, and he takes only one psychotropic medication. Which one of the following is most likely to be responsible?