supraventricular tachycardia
"I was prescribed metoprolol for tachycardia. I took it for about 6 weeks. I did feel better and not as fatigued, but suddenly I had severe depression. I felt like everything in my life was out of control even though mentally I knew it wasn't. I was sobbing hysterically all day and felt like I was losing my mind! I figured out the only change I'd made was taking metoprolol so I weaned myself off of it and the depression cleared right up. My doctor said he has a lot of patients on this medication and even though depression is a side effect none of them have had this issue. So I'm guessing it's not a common side effect but beware if you're just starting this."