Saw a thread and a bunch of questions on this so I thought I would share my border experience. You can bring across any anabolic steroid (and just about any "medication" for that matter) from Mexico for personal use. I am not sure how much qualifies as personal, but here is how it works and why, in laymans terms (I know cause I have done this before and live very close to the border):
1. you go over the border
2. find a licensed Mexican doctor
3. pay him to write a prescription out to you
4. go to a drug store/pharmacy
5. purchase the gear
6. and then prescription and gear in hand you cross the border.
They will let you across, but the prescription which you obtained in Mexico is no longer valid after you step into the US (meaning you are now in possession of the gear with nothing to cover your ass). It can be done daily if desired (there is only a limit to how much you can bring across/day). This is how it worked for me a couple months ago, but everything said, just ask any customs agent and they can tell you exactly how it works. Also, this worked for me WALKING back and forth across the border, not too sure about how it works FLYING (although one would think the same principles apply). The reason we can get away with this insanity is that so many people buy their prescripiton drugs across the border (and yes most gear has some valid medical use), and because the majority of Mexican doctors can be paid-off.
Hope I havent left anything out.
Once again, ask a customs agent on the way over BEFORE you purchase anything just to make sure that the laws havent changed, cause wierder s**t has happened.