(or any downer) is usually a bad idea, especially long term. If you need to do it once in a while, you should be okay.
Example: Lets say you take xanax
at night, the next day, it's still in your system but you can't feel it. You would likely need more adderall
to feel like you normally would, and this of patterning can lead to taking more than you should and increased heart rate without actually noticing any danger.
Also, if you take more than just .5mg xanax, you could end up forgetting not to take more, end up eating several, and not notice the negative effects from that until it's too late, because you are so wound up from adderall, and when that wears off, you could go into the xanax xombie state.
Good luck, just be careful. If there is anything else you need to know i'm sure someone else will post too