Thanks for asking at Healthcare Magic. I read your question and I understand your concern. Triamterene HCTZ is a combination of two diuretics used to control High BP(decrease BP) in people who has dangerous of lowering of potassium like people with Channelopathies. Also decreasing edema that is abnormal fluid retention in the body. As your friend was having low BP and this drug has further lower it down. When blood pressure falls due to drugs other substances that cause rapid fall, leads to reflex tachycardia that is mediated through cardiac nerves. Hence sudden decrease in BP leads to reflex tachycardia i.e increase in pulse rate. I would like to advise your friend to dig out cause for low BP i.e loose motions, myocardial infarction vasovagal syncope etc. Take plenty of fluids that is 8-12 glasses of water Avoid caffeine at night, and long time standing. wear elastic compression stocking if problem still persists. Hope it helps best Don t forget to rate this answer and close the discussion at Healthcare Magic Regards Dr Ejaz