In general I'd say no, but it depends on the drug. Opiates I cannot control my use, in that, if I have the money to continually use opiates, all the while knowing that doing so will leave me with a physicall Dependance, I will do so anyway. However, with opiates I am able to structure my addiction, meaning I can moderate when I get high, and when I get straight. When I was only using heroin, I usually had a schedule that was something like; a 3 bag shot in the morning (to get high), a 1 bag shot around lunch time, a 2 bag shot at 5-6 pm, and then a 3 bag shot before bed (often accompanied with some cocaine). I always made sure I had at least one shot in the morning but offten bought a little over a bundle each day as I savored that morning fix.
With cocaine I have absolutely no self control. I'm like a lab rat, and just do shot after shot until it is gone (which is why I have such a fear of this drug now.) I had similar experiencing with MDPV and 4-MCC. With Dextroamphetamine I actually do have control over my use, and I believe this is mostly due to the fact that I don't use this drug intravenously as there is no point. Shooting it dirties the high, and shortens the duration. Instead I use it rectally so I get great absorption and duration, but there isn't as much of a fiendish nature. In fact, I don't even feel "euphoric" so much, as I just feel "normal" but happy and motivated.
With benzo's I have little control over as well if I have access to large quantities of them, but I don't use them to get "fucked up" like some people do. I litterally take them for my anxiety, and always have started off at the lowest dosage possible to achieve the desired anxiolytic effect. The problem of course is that they work fucking fantastically but tolerance starts to develop fast, so while I may only need .25 mg of alprazolam initially to achieve a calm state of mind, I'll be taking 2 mg at a time a month later.
One strange thing Ive noticed about myself when it comes to my impulse control over using benzo's and opiates, is that I can offten "treat" myself (I hate using that phrase) to shooting heroin one day, and if I only buy enough for one shot, I can easily not pick up again for quite a while. But if I get enough heroin that I can get high two days in a row, well that's when I run into trouble.