A class of drugs called beta-blockers should no longer be used as routine to treat high blood pressure, says the NHS drugs watchdog for England and Wales.
Around 40% of adults have high blood pressure
Other drugs are better at treating the condition, also known as hypertension, which affects 40% of adults, it says.
The guidance from the National Institute for Health and Clinical Excellence says using beta-blockers can also increase the risk of diabetes.
But patients on the drugs are urged to keep taking them until seeing their GP.
The guidance, developed in conjunction with the British Hypertension Society, is an update of NICE guidance published in 2004 - but only the section on drugs for managing hypertension has been republished.
The hypertension guidance was not due for an update until 2009 but new research prompted NICE to take a fresh look.
In 2004 a large trial was stopped early because the results with newer drugs to lower blood pressure were so good.
About 40% of adults in England and Wales have hypertension and in 2001, the NHS funded 90 million prescriptions for drugs which lower blood pressure.
Two million people in the UK are currently treated with Beta-blockers for hypertension.
The drugs are also used to treat heart failure and angina and should still be used for these problems.
But NICE now says the evidence suggests they perform less well than other drugs in treating high blood pressure, particularly in the elderly, and there is increasing evidence that they carry an "unacceptable risk" of provoking type 2 diabetes.
Instead doctors should use another class of drugs, adding in different ones if a patient's blood pressure remains high, it says.
Black patients of any age or patients aged over 55 in all other ethnic groupings should be treated with a class of drugs called calcium channel blockers or drugs called diuretics.
If a person's blood pressure remains too high - the target is 140/90mmHg - they can take a second group of drugs called ACE inhibitors and if they need further treatment the GP can add whichever of the three the person has yet to take.
In patients under 55, first drug should be an ACE inhibitor, followed by a calcium channel blocker or a diuretic, then all three
In patients over 55, or black patients, first choice should be a calcium channel blocker or diuretic, followed by an ACE inhibitor, and then all three if necessary
Beta-blockers should no longer be used for hypertension except in patients who need them for other reasons such as heart failure
Patients under the age of 55 years should start treatment with an ACE inhibitor.
Professor Peter Littlejohns, clinical and public health director at NICE, said: "It is unusual for NICE to consider reviewing its guidance ahead of its planned review date. In this case, however, because significant new data became available, we took the decision to consider that data as part of a limited review."
Experts were quick to advise patients not to stop taking their medication and said a discussion should be undertaken with their GP at their next routine appointment.
Dr Mark Davis, a GP in Leeds and member of the guideline development group, said: "The most important thing is that we reduce the blood pressure and that's more important than the medication used.
"This guidance clarifies the best treatment options. But this is not an emergency."
Professor Graham MacGregor, chairman of the Blood Pressure Association, said: "High blood pressure is the most important preventable cause of death and disability in the UK.
"This is a major step forward. There are several million people on beta-blockers, but no one should stop their medication without advice.
"Probably 70 to 80%, over the course of the next year will be switched [to a newer drug] but it's not a panic situation."