As with any surgery you need to let the doctor know what medications you are taking, he should advise you of anything you need to do or change. Your operation may not have anything to do with your current medication but there are secondary things like pain killers, vitamins,anasteia, all of which may interact with what you take, never good to lie to a doc thats doing surgery. but seeing as how a vasectomy has nothing to do with hormal production you should be fine. All they are doing is either removing/tying hte tube that carries sperm to your urethra. So the amount, shape, size, color, smell, taste etc of your man load should not change just the fact that you cant have kids should. Thats why its called firing blanks, you get everything but the deadly portion coming out.
Which leads to me this, anybody ever read the back of Aspirin bottle and see that it sayd dont take while on steroids.