I think you are on your own on this one. Some medicatiosn in Mexico are more than likely safe while others may be questionable. I have been to Mexico hundreds of time (living in Texas) and I just can't force myself to accept their medications or medical services. I know people that have and they are more than happy. About customs. This is a tricky question. If you had a prescription then no problem with a reasonable amount. If you are carrying a large amount without a prescription and you are searched you should expect delays and a lot of questions and you will more than likely lose the drugs. If the particular drug is on the list of prohibited drugs then you are in big trouble at the border. I would not try to hide anything because if the agents don't find the item the dogs will.