Heroin stays in your system for approximatly 2-3 days depending upon freqency of use. I have been to different sites and they answer differently. I've seen questions regarding methadone and the time it stays in your system and they are totally wrong. They state 2-3 days when depending upon how much you use it can be detected for a long period of time. So it depends on your body weight and metabolism. But be on the safe side and wait 3 days just to make sure you don't test positive.