Its almost impossible for anyone to tell you the exact moment you will be fine to use heroin. In my case i could do heroin while drinking just as long as im not too drunk, or just do less dope then i would have to do if im a little bit to drunk to do my normal amount. All depends on how much you can handle alcohol, how drunk you are, your tolerance to dope, how much your planning on doing, etc..Just remember its always best to be safe then sorry, if you don't know if you can handle it or not just simply save the dope for when you don't feel drunk anymore. Opiates / opioid and alcohol can be a scary mix because they both slow down your respiratory system. Also both drugs will increase the strength of each other so you always have to take that into consideration when you choose amounts and time to use.