Modern, systematic interrogation methods are extremely effective. Probably only 1 in 1000 people would be able to resist in any meaningful fashion. Training only works if you are able to think clearly enough to remember and employ it, and if you are practiced enough in it that you don't have to try to dig through a hazed brain to remember the techniques.
Keep in mind that it would almost never be a simple matter of just injecting a drug into your system. They would also play games with lighting, sleep, food, your perception of time, place, and just about everything else. All of that can be handled mechanically and will dramatically affect your ability to think, your ability to control your emotions, your tolerance for discomfort, etc. Sooner or later you WILL break. No one can hold out indefinitely, and against a skilled interrogator using the full array of available chemical and psychological tools, it would probably take no more than a week to break even the most commited person....if we were allowed to go that far.
The problem is that the degree of mind-f*cking taking place is so severe that it's not opened up as a possibility too often. Sodium Amatol and Sodium Pentathol are also pretty effective. I cuaght myself saying some things I really wished I hadn't to an attractive nurse when coming out of general anesthesia once. That gave me pause.