Medicine shortages in the UK more than doubled between 2020 and 2023, while Brexit weakened the country's ability to tackle the issue, according to research by the Nuffield Trust.
Since leaving the European Union in January 2020, shortages have become the "new normal", including for antibiotics and epilepsy drugs, the thinktank said.
Drug companies issued notices warning of shortages more than 1,600 times last year, up from 648 in 2020, leaving the taxpayer having to reimburse pharmacies for buying more drugs above their normal cost.
Mark Dayan, Brexit programme lead at the Nuffield Trust, said:
"We know many of the problems are global and relate to fragile chains of imports from Asia, squeezed by COVID-19 shutdowns, inflation and global instability.
"Officials in the UK have put in place a much more sophisticated system to monitor and respond, and used extra payments to try to keep products flowing.
"But exiting the EU has left the UK with several additional problems - products no longer flow as smoothly across the borders with the EU, and in the long term our struggles to approve as many medicines might mean we have fewer alternatives available."
Between 2022 and 2023, four drugs authorised by the European Commission were approved faster in Britain, but 56 were approved in Britain after the EC and eight had still not been approved as of March this year.
The UK cannot rely on formal changes to the UK-EU relationship "any time soon", the report said, but there are steps the government can take.
These include being better at anticipating shortages and being more open about them, as well as being wary of sudden squeezes on cost driving instability.
Dr Leyla Hannbeck, chief executive of the Association of Independent Multiple Pharmacies, called for the Department of Health to review its procedures.
"Pharmacists are in the same position as patients - we are at the end of the supply chain but are not communicated with effectively by the officials.
"Consequently, we are unable to plan in advance and support the people who rely on us for their medications."
Paul Rees, chief executive of the National Pharmacy Association, said medicine shortages "have become commonplace", which is "totally unacceptable".
"Ensuring an adequate supply of medicines is surely a basic function of any modern health system.
"The solutions have to be international as well as national, but our own government needs to create the conditions for enough medicines to flow into and around the UK system, by properly funding the supply chain at both ends."
A Department of Health and Social Care spokesperson said:
"Our priority is to ensure patients continue to get the treatments they need.
"There are around 14,000 licensed medicines and the overwhelming majority are in good supply."