First off, you have to be in at least acute withdrawal before you take
suboxone or it will put you into precipitated withdrawal. That means wait till you feel sick and have some symptoms of withdrawal like a bad case of the yawns, goosebumbs, hot cold flashes, dialated pupils or whatever withdrawal symptoms are unique to you. Should be about 12-24hours after your last high. Then take either a quarter or a half a pill. If you feel better after 20 minutes thats your dose. If not take a bit more till the withdrawals subside. Then taper off whatever dose you go on. Its a great way to come off opiates without withdrawals. I was on H and my starting dose was 24 mg to get rid of the withdrawals but i had a huge habit. Your friend has done you right. 4mg should be good.
If you stay on the sub for more than a couple weeks you will be hooked on that, which is what most poeple use it for (Maintenance therapy). But it is excellent for short term outpatient detox. Tons of dr's prescribe it.
Hope that helps.