"The legal status and regulation of some medicines prescribed or bought in the UK can be different in other countries.
You cannot take some prescription drugs into the US. The US Food and Drug Administration provides information on bringing medicines into the US.
UK prescriptions are not valid in the US. To get pharmacy drugs, you need a prescription from a US provider (available from an urgent care facility, emergency room or a doctor)."
"Travellers should carry a copy of their prescription together with a covering letter from their doctor. If supplies are needed whilst abroad, a pharmacy or health care provider should be consulted for advice. "
"The legal status and regulation of some medicines prescribed or bought in the UK can be different in other countries.
You cannot take some prescription drugs into the US. The US Food and Drug Administration provides information on bringing medicines into the US.
UK prescriptions are not valid in the US. To get pharmacy drugs, you need a prescription from a US provider (available from an urgent care facility, emergency room or a doctor)."
https://www.gov.uk/foreign-travel-advice/usa/health
The fda link has been scrubbed and is page not found.
https://www.fda.gov/consumers/consumer-updates/5-tips-traveling-us-medications
"Travellers should carry a copy of their prescription together with a covering letter from their doctor. If supplies are needed whilst abroad, a pharmacy or health care provider should be consulted for advice. "
https://www.travelhealthpro.org.uk/factsheet/43/medicines-and-travel
Currently you can take misoprostol, mifepristone and birth control pills out of the UK but who knows if you take it into the USA.
So yeah its a mess and its going to cause problems.