By CNS drugs do you mean psych drugs or, say, centrally acting alpha 2 agonists? For me, the psych drugs just required a lot of memorization, since we had to learn each individual drug instead of just classes. For the ANS drugs, and many other chapters, I strongly disagree with just memorizing what they do. Learn how the ANS works. Write down, over and over again, what the effects of the sympathetic and parasympathetic branches do to various parts of the body. Make lists, charts, pictures, flashcards, whatever helps you to learn. You also need to know the receptor types and where they are. The rest should fall into place once you think about it. Beta blockers, for example, block the action of the sympathetic nervous system at the heart and lungs (unless they're cardiospecific, and only block beta 1 receptors). At the heart, the symp increases heart rate and force of contraction, thereby increasing cardiac output. A beta blocker, then, slows down both of these so the heart doesn't have to work as hard. At the beta 2 receptors at the lungs, the symp system dilates the bronchi. Therefore, beta blockers constrict them. What's a possible adverse effect? Well, you want to use caution giving these to asthmatics or COPD patients. Most of this follows if you really know your physiology. I got an A in pharm last semester and didn't think it was all that tough, but I did study my rear end off. You have to know the physio, because you do have to retain this stuff all the way until the NCLEX. That's just my two cents.