your mind is under the control of that substance
I think this is a purely metaphorical statement, which is meaningless if taken literally. Drugs change the physical structure of your brain, they dont ‘take control’.
Volition does not allow a person to do ‘whatever he likes’ - this would make it almost occult. It allows him to choose between the limited range of options which are available to his mind at any given time. The chemical effects of drugs can modify the options available, and they can also modify how attractive each option seems. But they cannot make the choice for you.
I dont think drugs are special at all - normal human ‘moods’ have the exact same effect, although to a lesser degree. Let’s take an example. Imagine that you are in a good mood, sitting on a bus on your way to work. A baby starts crying loudly, which irritates you immensely. You start considering what to do, and several options enter your mind - you can ignore it, you can ask the mother to quieten it down, you can go and sit upstairs, you can get off the bus, and so on. These options will be ‘consciously available’ - they are things you are explicitly considering, and your volition consists in choosing between them.
Now lets imagine the same situation when you are in a bad mood. You had 3 hours of sleep last night, youre late for work, and you just managed to spill a can of coke all over your nice clean shirt. In other words, you are highly irritated and close to breaking point. What options will enter your mind now? Well, most of the above ones will also occur. But you might also start thinking exceptionally dark thoughts, perhaps involving getting up and punching the baby, or maybe even throwing it out the window. These thoughts horrify you, and you try to put them out of your mind. Of course, you do not actually carry them out - you are not the kind of person who would intentionally harm a child.
Now, in the second situation, I would say that you are exercising volition in not harming the child. The option is present in your mind, you are fully aware you could choose to carry it out, yet you decide not to. However in the first case, you arent choosing not to harm the child. There is no sense in which you are considering ‘should I hurt the child or not?’ like you would be in the second case - you havent even considered it as a possibility, it is not an option available to you, and it is quite literally not in your mind. Some people might say you are ‘subconsciously’ or ‘implictly’ choosing not to harm it, but I would say these expressions are meaningless unless you want to give them some sort of definition.
Another example would be someone who has just learned that there is something humans can do which he wasnt previously aware of. Imagine something silly, like rolling your tongue or wiggling your ears, and also imagine that you had never done this, or seen anyone do it. Now, one day your friend tells you about this “really awesome trick” he has discovered, and shows you his tongue rolling. Suitably impressed, you now try it yourself and find you can do it too. From this point on, you have the option of choosing whether to wiggle your ears. But before you found out it was possible, it doesnt make sense to say you were ‘choosing’ not to do it - you didnt even know that tongue rolling existed and it was never an option available to you.
Now, humans dont explictly choose what enters their conscious mind. Their choice consists purely in deciding between the alternatives that they ‘somehow’ find before them. If you dont believe this, go and try the standard meditation trick of sitting absolutely still, and trying to think about ‘nothing’. Observe how random unrelated thoughts suddenly pop into your mind without your conscious control. Why did you just think of a holiday you were on 7 years ago? Who knows.
Or, imagine trying to chat up an attractive girl - you saw a TV program last night where some lothario charmed the pants off some girl in a bar, and you wish to do the same. But you cant - the right words just arent coming into your head. Whereas his dialogue flowed gracefully, yours sounds awkward and stunted. You desperately want to talk like a ‘big shot’, but you simply dont have this option - the right words arent available to you and no magical act of volition is going to help you out. You can of course choose between the options which do enter your mind (you can tell her she has nice eyes, or decide not to), but you cant choose to say the beautifully poetic lines which you havent (non-volitionally) thought up.
Once free-will is understood in this way, the problem of whether “drugs control people” disappears. They dont - drugs simply change the options you have available at any given moment. When you are on an LSD trip, you will have possibilities enter your mind which would never EVER EVER have occurred otherwise. When I stand near a window normally, I don’t ‘choose’ not to jump out it - this possibility doesnt even enter my head for a split second. But under the influence of LSD, jumping might be something I would actually consider. My volition still exists and I am in no way determined - I can still choose whether to jump. But the choices available to you are not the same.
edit: Above I said “humans dont explictly choose what enters their conscious mind”. I want to stress the ‘explicit’ part - there are certainly ways of making yourself more likely to have certain options available. While I might not have had the poetic words to charm the girl available last year, I might have them now as a result of deliberately choosing to learn how to speak more eloquently. And of course choosing to take LSD will allow ‘weird’ things to enter my head, even though I dont actually choose which weird things they will be.