Concerning a potential withdrawal agreement
The UK government and the 27 remaining EU member states agreed in November 2018 on a withdrawal agreement laying down the conditions and rules for how the UK is to leave the EU. In October 2019, the UK government and the remaining 27 EU member states agreed to revisions of parts of the agreement. You can find the withdrawal agreement on the website of the European Commission.
The agreement establishes a transition period, which will start on the withdrawal date and end on 31 December 2020 with the possibility of a one-year or two-year extension. During this period, the UK will no longer be a member of the EU and therefore not represented in the EU institutions, but all the rules of the European Union will continue to apply to British citizens and businesses. The rules on the free movement of goods will still apply to all goods including medicines. Any good placed on the market in the EU or the United Kingdom before the expiry of the transition period can still be placed on the market in the EU and the United Kingdom and circulated between these two markets until it reaches its end-user.
The transition period will allow for negotiations on the future relationship between the EU and the United Kingdom.
However, for this to happen, the withdrawal agreement will need to be approved by both the UK government and the European Parliament before the withdrawal date of 31 January 2020.
EMA (European Medicines Agency)