Some of the world's biggest pharmaceutical firms have warned the government a no-deal Brexit "poses a serious risk" to the sector.
Written evidence submitted to the Business, Energy and Industrial Strategy (Beis) committee raises "serious concerns" about the effect of the UK's exit from the EU on the sector, chair Rachel Reeves said.
The cost of medicines and investment into Britain's pharmaceutical sector could also be harmed.
The evidence from 19 leading institutions and companies from the sector is being published ahead of a public evidence session on Tuesday.
"Falling back and relying on World Trade Organisation (WTO) rules... poses a serious risk to patients as medicines and diagnostic tests reach patients via a fragile supply chain," wrote Swiss firm Roche.
Astrazeneca said providing "frictionless" trading was "critical for our global supply chains, imports and exports of raw materials, clinical trial materials and samples".
Merck, which last week picked a central London site for its new European base, said the government's negotiation should ensure "specific provisions" are made to ensure skilled EU staff can be access by the UK pharmaceuticals sector.
Reeves said she was looking forward to hearing further evidence this week to feed into the government's Brexit negotiations.
There are serious concerns raised around the future regulation of pharmaceuticals, mutual recognition of medicines, and the prospect of damaging disruption to cross-EU drug supply chains. This is very concerning, with uncertainty risking the UK becoming a less desirable place for investment and development in a growing, productive industry.