Obviously seek professional medical opinion and advice rather than relying on what is said here, but for me in my experience I am prescribed 20mg Tadalafil and the GP said it was OK to cut them in half, so 10mg effectively. As PhelTGrik states they have a long half life and I find for me that they are best taken about 12 hours before a punt. I used to take them 2 hours before but more often than not they would not work, went back to the GP and she said try 12 hours before and they are successful every time. You'll need to experiment to find what works for you but 20mg for me 12 hours before is worse, lots of side effects. 10mg 12 hours before zero side effects and I'm rock hard when needed 12 hours later. One of my regs was 3 hours late once and it still worked, so 15 hours after taking half a 20mg tablet. Good luck!
