IV heroin is 100% BA and gives you the full effects of the heroin,all at once.smoking does waste a % of the heroin ,depending on how you smoke it ,but you definetely lose 30-40% maybe at least when smoking heroin,and you are not getting all of the heroin at one time,versus IV injection,where none is wated and you get your dose at one time,hence the better high and all that.It is similar ,although not much ,with smoking crystal meth vs. injecting meth: You may not waste much when smoking meth ,but you are taking a series of many hits while smoking ,which takes time to build up in your system.Injecting the same amount of meth is getting all the meth in your blood at once,vs over a period of time.IV use of any drug means you get a high very quickly,get all the drug in your bloodstream without any waste and gives a stronger more immediate high rather than a more time consuming slower to reach full blood levels when smoking,not counting any wasted vapors/smoke.