How Does Metpure-XL Work And What Are Its Side Effects?

My Doctor has given me METPURE-XL 25 as I am feeling uneasy all the time and scared to go in dark , room without window and closed lifts. My ECG is ok except my heart rate is slightly high about 90.My BP is usually normal but at the time of taking ECG it was 130/90. Can you tell me what this medicine will do and is there any side effect.