I spoke with a pharmacist today about drug shortages and she explained some things about the drug shortages.
The drug wholesalers don't have a warehouse in each country as people might imagine - they each have a single distributed warehouse across the EU. Some drugs are kept in some warehouses, and others in other warehouses. When your chemist orders something they don't have, it arrives next day (and sometimes same day), but may well have come across the channel. There's a continuous flow between the warehouses and pharmacies, a large amount across borders.
When the government suddenly prevents export of a drug (such as medroxyprogesterone, as they did a couple of weeks ago), that completely screws up the distribution of that drug across the EU, because if they happened to be storing it in the UK, they can't get it to pharmacies outside the UK anymore. To avoid this, they stop storing such drugs in the UK where they will get stuck, and then supply all UK requests from foreign warehouses. Actually, they've stopped storing lots of drugs in the UK in anticipation of more export bans, and because of not knowing if they will be able to move stock without incurring import duties going across the channel.
The drop in the pound has a significant impact because the NHS agrees to pay a certain amount for each drug, and when the pound falls, the suppliers get less for supplying to the UK than supplying to the Eurozone countries, so when stocks are limited, they go to Eurozone countries who are effectively paying more. The NHS has a process for renegotiating prices when this happens, but as you might expect, it doesn't happen quickly.
Pharmacists are getting the odd packet of medroxyprogesterone in, but can't satisfy requirements, not helped by no one holding any stock in the UK anymore.
Alprostadil has a significant shortage issue too:
Muse unavailable with no info on when it will reappear.
Caverinject: 10ug only can be obtained.
Viridal: 10ug and 40ug available.