Depends upon the opiates/opioids in question. Heroin is usually totally clear from your system within 3 days. If you want to avoid dependence and subsequent withdrawals then I'd suggest waiting for at least another 3 days after that before you use again - so at least 6 days after your last use. This is not based upon any scientific evidence I hasten to add, just personal experience. Unfortunately, this takes a lot of self discipline to achieve, especially if you have ready access. I would also recommend an extra 3 days of abstinence for every consecutive day you have used. E.g. If you have used for 2 consecutive days, allow 3 days for it to leave your system, then 6 more days for any tolerance to drop - 9 days total. If you've used for 3 consecutive days, allow 3 days plus another 9 days to 'reset' - 12 days total. I could never stick to this regimen and suffered greatly for it...