High blood pressure is a widespread problem
Doctors say it could potentially save the lives of tens of thousands of people each year in the UK.
Beta blockers are known to reduce the risk of stroke by 40% and of a heart attack by 20%.
But losartan was found to reduce the risk of stroke by a further 25%. It also cut deaths from combined heart attack and stroke by a further 13%.
The drug also produced fewer side effects.
Already available
Losartan is already available on the NHS, but doctors believe it should now be used on a more widespread basis.
"Hypertension is an enormous problem affecting 10 million Britons and is the single most preventable cause of stroke.
"Up until now the guidelines have been to prescribe older drugs such as atenolol because there has been no evidence to show losartan has additional benefits.
"From today onwards GPs should seriously consider why patients should not receive this drug."
Eve Knight, director of the British Cardiac Patients Association said the results of the trial were good news for patients, their families and carers.
She said: "The results of this are set to dramatically and positively affect the way high blood pressure is treated in the UK."
Eoin Redahan of the Stroke Association said the results were "extraordinarily exciting".
Losartan costs £18.19 per month compared with £5 for atenolol.
However, the Stroke Association said the cost should be weighed against the potential savings in treating stroke patients.
The research will be published in The Lancet.