Millions of patients are being overtreated for indigestion with expensive drugs that cause side effects and are unnecessarily costing the NHS at least 100m a year, experts say.

Doctors are reaching for the "top weapon in the armoury" to treat even mild cases of indigestion when a simpler, safer, cheaper alternative would do, they say.

The drugs proton pump inhibitors stop the backflow of acid into the stomach but cost two to three times as much as other prescription remedies for indigestion. They carry an increased risk of pneumonia, osteoporosis and kidney problems and double the risk of infection with C.difficile, the superbug.

Ian Forgacs, consultant gastroenterologist at King's College Hospital, said the overuse of the drugs was "poor medicine" and was draining the NHS of funds.