AstraZeneca’s boss has warned of major healthcare changes in the US after Donald Trump’s surprise election victory.

Pascal Soriot, chief executive of the UK drugmaker, said the Affordable Care Act, known as Obamacare, which has helped millions of Americans get health insurance, was likely to be scrapped or substantially altered once Trump takes office. The Senate’s majority leader Mitch McConnell said this week that Republicans would move quickly to roll back the legislation.

Drug stocks surged on Thursday as fears of tough action on medicine prices faded. Hillary Clinton, the Democrat presidential contender, had vowed to tackle high pricing.

However, Soriot was cautious, saying “price pressure … is not going to go away”. He told reporters: “Nobody knows what the new landscape will look like. It’s reasonable to assume it will change substantially.

“What we can reasonably expect is that the Affordable Care Act will either be repealed or substantially modified.” He said he hoped that any changes would still support innovation and the development of new medicines.

His comments came as AstraZeneca reported weaker than expected sales for the third quarter. Revenues fell by 4% to $5.7bn, hit by cheaper generic versions of the group’s cholesterol pill Crestor.

Earnings benefited from a one-off tax payment of $453m, owing to agreements on transfer pricing between the UK, Canada and Sweden. This meant core earnings per share rose by 28% to $1.32. The company has also been cutting sales and administration costs but expects research spending to be higher this year than last.

Soriot reiterated that the company remained on track to return to growth in the second half of next year, adding that there would be no patent expiries between then and 2024.

The new cancer drugs Tagrisso and Lynparza are performing well. Tagrisso is expected to be approved in China, which has a high prevalence of non-small cell lung cancer, sometime next year after receiving a priority review.

AstraZeneca suffered a setback last month when the US regulator ordered it to halt clinical trials of its new immunotherapy durvalumab as a treatment for head and neck cancer following bleeding incidents. Other trials are continuing, and data on a combination with another new drug, tremelimumab, to treat lung cancer are expected in the first half of next year.

Soriot remains under pressure to deliver, following the board’s rejection of a £69bn takeover offer from Pfizer in 2014. AstraZeneca shares dropped by 4.6% to £43.67 on Thursday – below the £55 price offered by the US pharmaceutical giant.