A common medicine, Accuretic, taken to manage blood pressure is being recalled after it was found to contain a carcinogen.
Pharmac says almost 36,000 New Zealanders using the medicine will need to change treatments, although it says the health risk is very low.
Pfizer supplies the medicine, Accuretic, which has also been recalled in other countries including Australia, Canada and the US.
Pharmac's director of operations Lisa Williams says they have been working with Pfizer over the past few months to see if a substitute will be available.
"Unfortunately, because it's a global issue, no alternative brand is available in sufficient volumes for New Zealand and that can be verified as being free from contamination," she says.
"This means there is currently no acceptable direct chemical substitute for New Zealanders taking this medicine."
Williams says there are two funded alternatives with sufficient stock, losartan with hydrochlorothiazide and angiotensin-converting enzyme inhibitors or angiotensin receptor blockers.
"We want to ensure, first and foremost, that patients can continue to access funded treatment," she says.
"Medsafe has advised us that there is a very low risk to people who are taking Accuretic, and they should continue with their treatment because the risk associated with suddenly halting blood pressure medication exceeds that presented by the contaminant."
People taking Accuretic are being advised to consult their doctor about an alternative treatment when their next prescription was due.
Pharmac will cover the cost of the GP clinic visit and prescription fees.
"We know that our healthcare sector is currently under a huge amount of strain, and that changing this many people to alternative treatments will add to that strain," Williams says.
"We are asking clinicians to move their patients to alternative medicines as soon as possible, and we really appreciate the support that we know that both clinicians and pharmacists will provide to their patients."