The Government's drug-buying agency Pharmac has signed a deal for the heart drug metoprolol which it says will save the country $65 million over five years.
About 200,000 people take the beta-blocker which is used as a treatment for high blood pressure.
Until now, it has been supplied by solely by AstraZeneca under the brand name Betaloc.
Pharmac has signed an agreement with a competitor AFT Pharmaceuticals and renegotiated its deal with AstraZeneca.
Acting chief executive Steffan Crausaz says the saving will be one of the largest in the agency's history.
Pharmac will pay the same subsidy for both brands of the beta-blocker, meaning patients will not have to change brands unless they want to.
Mr Crausaz says the deal has also lowered the price of Goserelin, a drug used to fight prostate cancer, and that medicine will now be more affordable.