Millions of people who take common indigestion drugs could be putting themselves at increased risk of heart attacks and strokes, according to US medical experts.

The drugs, known as ‘proton rise inhibitors’ (PPIs) can cause an increase in unhealthy substances that trigger hearts attacks and strokes.

PPIs include drugs with brand names such as Zanprol, which is sold over the counter without a prescription, which work by blocking the production of stomach acid. They are intended for short-term use but many people use them ..

However, scientists at the Methodist Hospital Research Institute in Houston, Texas, have discovered that these drugs block the release of nitric oxide, a gas which helps arteries to stay flexible.

The researchers said: “Several studies have raised concern that the use of PPIs in patients with acute coronary syndrome ie heart disease may increase their risk of major adverse events.

“We found plausible biological mechanism to explain this.”

Another study in the UK found that PPIs also stopped the body from absorbing calcium, resulting in users having a 44% more likelihood of suffering a hip fracture.