Desertshores already posted the details:
The personal importation exemption still exists but never did apply to any FDA approved drugs that are available in USA. Those of us whose medications from India were intercepted in past years received a notice listing the official personal importation rules (for release of the medication), which includes requirement that the drugs not be available in USA, limited to 90 days and provide either a US doctor’s prescription or a letter signed by the US doctor stating you are under their medical care and they are aware you are using this medication. For foreign citizens NOT resident in USA, the exemption extends to all medications, including those available in USA. The consensus on this board was that it was impossible to meet the requirements for rapamycin for US citizens/residents.
However there used to be a discretionary exception made by Customs for packages with up to 90 days of medication, which supposedly was ended on July 9, 2025. Of course this discretion only applied to packages that were inspected, and was not guaranteed, even in past years : In past years I have had one rapamycin package intercepted with the above mentioned letter (I just abandoned the package) and another rapamycin package had clearly been inspected by customs but was let through (after a 2 week delay). Most other packages of mine from India don’t appear to have been opened, the likelihood of inspection is pretty low. The complication now is that unless the seller in India misrepresents what is in the package, a package with declared medication on the customs form will theoretically be intercepted automatically.