ive bn a user of heroin n methadone for 6yrs now n just recently had problems try'n 2 find a vein n stuff but now when i find a vein (shoot'n methadone mainly) n the blood starts cum'n bak up the butterfly i push it in 2 hav my shot but as soon as my blood gets inside it, it blocks my butterfly....BASTARD!!...lol.....i dont no y this happens is it my blood cloting that quick or wat the hell is it?? if sum1 could pls answer this it would b muchly appreciated!! THANX!!