The European Medicine Agency (EMA) announced in November last year it would move headquarters to Holland to avoid disruption to its operation because of Brexit.
Remainers warned the move would cost Britain jobs as the EMA employs around 900 people to oversee the safety of medication for nearly 500 million people across the European Union.
But executive director Guido Rasi told Bloomberg the agency is now bracing for larger-than-expected staff losses as a survey carried out last year showed only 19 percent of employees would be willing to move from London.
Mr Rasi said: "The level of uncertainty is still high because of practicalities. We are monitoring it on a daily basis.
EMA•GETTYBrexit news: EMA director Rasi said the agency could see bigger staff losses than expected
"There will be a dip but we will be back and we will be back as strong and as good as ever."
The EMA is charged with assessing the effectiveness of new medicines before EU sale is allowed and