Metoprolol
"I have SVT and high blood pressure. After 10 years the dr. switched me to Metoprolol from Atenolol. The medication works great with one caveat - you MUST check which brand you're getting.  The dr. changed my dosage, which resulted in different dosage pills. Suddenly my blood pressure jumped and my heart was beating erratically, chest pains (which I've never had), and I was constantly worn out. I checked the brands of the former medications and the new and found they were different. I switched back to the old meds at the new dosage for a couple of days and within 1 day my blood pressure dropped 20 points and I felt back to normal. Now the pharmacy special orders the Mylan brand, as the Aurobindo doesn't work at all."