Hi folks, I started taking the Sildenafil drug, prescribed by the hospital, on Saturday. I had to call the gp doctor as an emergency yesterday due to very very bad lower back pain. Nowhere does it read on the leaflet that came with the drugs about this side effect but the gp said it's a known one. Has anyone else suffered with it? It really affected my movement and couldn't stand, sit or lay down, this after only taking it for only 4 complete days. Look forward to some help on this please.