A new once-daily pill could help control blood pressure in millions of people in the UK whose levels remain high despite being on other medications, researchers have said. The drug could potentially help treat as many as 10 million Britons, and up to half a billion worldwide.

Baxdrostat, made by AstraZeneca, works by blocking an enzyme responsible for producing aldosterone, a hormone that regulates blood pressure and the amount of salt in the body. The global BaxHTN trial, led by Professor Bryan Williams of University College London (UCL), included almost 800 patients from 214 clinics worldwide.

After 12 weeks, patients taking baxdrostat saw their blood pressure fall by around 9-10 mmHg, which researchers suggest is large enough to slash the risk of heart problems. High blood pressure can be caused by a variety of factors, both genetic, for example by being overweight, and environmental, such as eating fatty and salty foods or drinking too much. If left untreated the condition can lead to serious cardiovascular issues.

Elsewhere, about four in 10 patients on baxdrostat reached healthy blood pressure levels, compared to fewer than two in 10 in the placebo group. Prof Williams, chair of medicine at UCL, said the findings suggest the drug "could potentially help up to half a billion people globally - and as many as 10 million people in the UK alone".

He said: "High blood pressure affects 1.3 billion people globally, and we know that it remains the most important preventable cause of premature death, principally from heart disease, stroke, kidney disease, but also increasingly implicated in dementia as well.

"For a number of years, the sense was that there was no need to develop any more drugs for treating high blood pressure, because we had enough drugs.

"But what nobody was taking into account is that the drugs we've got are not yet achieving the kind of control rates that we want. So it's really exciting to see that there are new drugs being developed in this field, because they're sorely needed."

High blood pressure is very common, with an estimated 14 million people in the UK estimated to have the condition. It often has no symptoms, and if left untreated can cause serious problems like heart attacks and strokes. Prof Williams said experts have only realised in the last 10 years the "really important role" aldosterone - which was discovered at UCL in 1952 - plays in the development of hard to control blood pressure.

"Unless we take this system out in some way, it becomes difficult to get blood pressure controlled in a very large number of people," he added.

"What had to happen is we had to inhibit the production of aldosterone and get it back down to a normal level, so that patients didn't have this high level circulating. And by getting the aldosterone level down with these drugs, we've seen blood pressure come down spectacularly."

Targeting aldosterone in this way could not only control blood pressure more effectively, but also result in the use of fewer drugs, Prof Williams suggests.

Sharon Barr, executive vice president of biopharmaceuticals R&D at AstraZeneca, said the findings - published in the New England Journal of Medicine and presented at the European Society of Cardiology Congress in Madrid - "demonstrate baxdrostat's potential in tackling one of the toughest challenges in cardiovascular care".

She added: "We look forward to advancing our regulatory filings for baxdrostat with health authorities in the months ahead, in addition to rapidly progressing a robust clinical development programme across indications where aldosterone plays a key role, including chronic kidney disease and heart failure prevention.