I posted several times regarding EU Notices and Notices from EU regulatory agencies. These remind that the UK will be a third country (as respects the EU) on exit at 12pm CET 29th March 2019. If you have not already done so, please read these Notices.
Any Transition Period that is agreed is in the context of the EU-UK Withdrawal Treaty, and will continue certain EU arrangements only.
One of the aspects is UK membership of EU regulatory agencies (third countries are not members of EU regulatory agencies).
On 11th April 2018, the European Medicines Agency (EMA) confirmed that the EU27 member states and the EMA had completed the task of redistribution of the UK portfolio of centrally authorised medicine and veterinary products. The UK will not be a member of the EMA on its exit. Arrangements were already in place to relocate the EMA (from the UK) to an EU27 member state.
Please read the information that is published about this redistribution here.