The Swiss pharmaceuticals company Novartis has said it is stockpiling drugs in the UK before a possible no-deal Brexit, which it warned would be “hugely impactful” for patients.

Firms across the economy are bracing for the possibility of the UK leaving the EU on 29 March without a deal after parliament resoundingly rejected Theresa May’s withdrawal agreement.

The Basel-based company said on Friday it imported 120m packs of medicines to the UK from the continent each year but suggested a no-deal Brexit would affect supplies.

“Following parliament’s vote, the risk of the UK exiting the EU without a deal is increased and this will be hugely impactful for patients, particularly around the supply and safety of medicines,” it said in a statement.

“We are building increased inventories across our portfolio of medicines in the UK.”

The French cosmetics company L’Oréal, owner of brands ranging from Lancôme to Maybelline, also revealed on Friday that it was stockpiling products in the UK in preparation for Brexit.

Novartis, the world’s fifth-biggest drugmaker by revenues, makes a large number of medicines ranging from treatments for cancer through to anti-inflammatories, including Voltarol, and the Ritalin drugs used to treat attention deficit hyperactivity disorder (ADHD). It is a major supplier to the NHS.

Novartis called for the government to “implement a comprehensive continuity plan rapidly” to ensure drugs continued to reach patients, with a particular focus on clarity of customs arrangements and minimising disruption at the border.

Pharmacists have been told that the NHS is preparing for the use of alternative transport routes and the prioritisation of medicines as part of Brexit contingency planning.

The head of the UK’s pharmaceutical association warned in October that stockpiling by companies would not be enough on its own to cope with leaving without a deal.

Martin Sawer, who leads the Healthcare Distribution Association, said patients might need to think about ensuring they had enough of their own stocks, although NHS bosses have warned this could itself lead to shortages.

Novartis urged NHS trusts and pharmacists to refrain from stockpiling medicines so supplies could be managed centrally. This would minimise “the risk of medicine shortages across the UK”, it said.

A spokesperson for the Department of Health and Social Care said: “We recognise the vital importance of the medicine supply chain as we exit the EU.

“The government has secured additional capacity on a variety of routes including ferries into and out of Poole, Portsmouth, Plymouth, Immingham and Felixstowe, where medicines will be prioritised.

“We have asked manufacturers to build up six weeks’ additional stocks of medicines and we are confident that, if everyone does what they should do, the supply of medicines will be uninterrupted in the event of exiting the EU without a deal.”

Novartis, which currently employs 1,500 people in the UK, also warned that regulatory divergence between the UK and the EU after Brexit would have “far-reaching implications for the way the life sciences sector operates and its ability to develop and deliver medicines for UK patients”.