Jenny Tait will do "anything" to keep her son alive.

She and her husband Peter are paying $396,000 per year to fund the "miracle drug" Trikafta for their 41-year-old son Isaac Tait who has cystic fibrosis.

But the "cruel and heartless" part is $52,000 of that is GST.

"We will do anything to keep our boy alive but absolutely detest having to pay tax to do so."

Cystic fibrosis is an ultimately terminal condition that affects about 540 people in New Zealand. Trikafta treats its underlying cause but is not publicly funded here.

The Taits are speaking out against paying GST on it, after Tauranga man Paul Cherry called for GST to be removed from the price of cancer medications that are not publicly funded. Cherry has spent $212,000 so far on a drug that is helping him fight prostate cancer.

However, a spokesperson for Finance Minister Grant Robertson said there were no plans to make changes to GST and there were better ways the Government could help target need.

Meanwhile, Pharmac said Trikafta remained a medicine Pharmac would like to fund, subject to available budget.

Whakatāne cystic fibrosis sufferer Isaac Tait says charging GST on Trikafta is "an absolute crime". Photo / Andrew Warner

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Isaac Tait lives in Whakatāne with his wife Britney and 15-month-old son Leo. He has been taking Trikafta for just over one year.

But Tait feels like a "burden" on his parents who are paying $396,000 per year on Trikafta out of their retirement savings.

"If I didn't have a son, I just honestly don't even know if I'd take this drug," he said.

Tait said his childhood was "absolutely horrific" - having cystic fibrosis was like "breathing through straws" and he had spent a total of about four and a half years in hospital.

"Prior to Trikafta, my lung function was declining. It was down to about 49 per cent," he said.

"And then all of a sudden it was like being in a wheelchair all your life and then just being able to stand up and run."

Tait said Trikafta had been "an absolute miracle drug". However, charging GST on it was "an absolute crime".

He has spent 17 years collectively volunteering at the local Coastguard, fire brigade and fishing club.

"I've given back to the community," he said.

"A lot of the time I think why the f*** do I bother when the Government's not helping me in any way, shape or form."

41-year-old Isaac Tait wants to see his 15-month-old son Leo finish school. Photo / Andrew Warner

Asked how much longer his parents could keep paying for the drug, Tait said he did not know, but going off Trikafta was a "scary thought".

"My lung function would start to plummet again."

Tait said it was "heartbreaking" to consider moving overseas to somewhere Trikafta was publicly funded, as his family was in New Zealand.

"That's not even fair either but yes if it came down to it, I'd just have to move to Australia and maybe fly home whenever I could afford to - I don't even know what I'd do there in the first place."

Tait said it made no sense Trikafta was not publicly funded. Before Trikafta, he was taking more than 30 pills per day and using two inhalers and nebulisers. Trikafta was just three pills per day.

"I want to at least see my son finish school and I want to see other kids just not have to go through what I've been through."

Isaac Tait has been taking Trikafta for just over one year. Photo / Andrew Warner

Tait's mother, Jenny Tait, said having a son with cystic fibrosis had been a "cruel journey".

"When he was born and he was diagnosed, we said he's not going to die of cystic fibrosis... And that one day they'll find a cure.

"And now we've got the miracle, we never ever thought though it would be denied access to it."

She said paying GST on Trikafta was "cruel and heartless".

"Even if we could pay it without the GST on top, that would help extend it.

"That $396,000 we're paying a year - who can afford that normally? We're retired and we sold our business so we're eating into our retirement fund to do it. Very, very few people can do that and we can't do it for long either.

"If you've got a child, you'll do anything to keep them alive and try and deliver a relatively normal life."

Jenny and Peter Tait are the previous owners of White Island Tours.

In a statement on September 23, a spokesperson for the Finance Minister said there were no plans to make changes to GST to allow more exemptions.

"GST exemptions are complex, create distortions and would take some time to implement.

"There are better ways that the Government can use to help target need. In Budget 2022 we made the largest single contribution to Pharmac's Medicines budget ever, [bringing] total funding to $1.2 billion.

"While Pharmac independently make decisions on the medicines that are funded, the Government will continue to invest heavily in the health of New Zealanders."

Pharmac is not responsible for GST on unfunded medicines, however, its director of operations Lisa Williams has previously said Trikafta was a medicine Pharmac would like to fund, subject to available budget.

Williams said there were 79 treatments on its options for investment list and, so far this financial year, Pharmac has made 18 new investments with more to come.

Williams said Pharmac had met with the supplier and manufacturer of Trikafta, Vertex, to reiterate its commitment to securing public funding for the drug.