It is perfectly legal to declare prescription, controlled, FDA-approved human drugs at a land border.
However, you are limited to what is approved by the FDA for human use....Mexican-equivalents would be Primosteston, Testoprim, Proviron, Deca, HCG (maybe some others).
Most of the good, cheap stuff though....the vet gear is not legal unless your "animal" is accompanying you.
Something like Boldenon by law should have been confiscated b/c it is veternarian horse anabolic with no medicinal human use here in the US. I don't doubt Bobber brought it back, since they probably didn't know what it was.
SOLID:
There is no human-grade Anavar that I am aware of in Mex.