In my expierence AT LEAST 8mg was necassary to overcome the worst of the symptoms. I was snorting anywhere from 4 bags to a jab a day. The initial breakthrough dose is usually the highest of your entire regiment. Almost everyone I know was given at least 8mg. ( sometimes 4mg and then 4mg more shortly thereafter) I have also been in your situation in terms of dosing heroin after a 4mg suboxone did not do the trick. I had 4mg on hand but ended up buying dope once I couldent take the symptoms any longer. From what I understand, the heroin will pull you out of withdrawal, but because your receptors are still occupied by the subs you will not get high. Did you feel worse after taking the suboxone? If so then you must consider that you may have dosed the suboxobe to early and you put yourself into precipitated withdrawal. I highly recommend waiting at least 24 hours, preferably 36. When you took the initial 4mg were you to the point that your couldent take it any longer? Ideally thats where you want to be. Did your doc perform the cows scale. He should have before administering the first dose. Cows stands for Clinical Opiate Withdrawal Scale and is a great tool for pinpointing the severity of your withdrawal. Good luck my friend, once you get your dose tuned in you will be amazed at how well suboxone works