it all depends, the general rule of thumb is 24 hours after ur last heroin use, but if ur a chronic user, u may have a lot of build up in ur system, and if ur not much in opiate withdrawl ur setting ur self up for a disaster of precip WD...but if u insist, take very very small amount, like a quarter of a sub or LESS, and SUBLINGUAL only. dont snort it or IV it...take baby amounts..if its been 48hrs, at the worst u should go thru a very light mild precip WD for an hour or 2, try take half of a quarter (1mg) wait 40mins, and see how u feel, if u feel uncomofortable, but managable that means ur going thru light precip, which is good, that means hours later u can start dosing sub..
by the way, just cuz its been 48hrs and ur not feeling withdrawl, doesnt necessarily mean its unsafe to take, u may not even be physically addicted to the heroin..which its safe to take subs after u take an opiate if ur not physically dependent on it (example: i am on subs, and do dope maybe like a few times a year, the next day ill take subs and be fine, cuz my body is only dependent on subs, not opiates, which precip wont apply to u)
