Alzheimer's patient Heather Cameron wants to be one of the first in line for a newly funded medicine to treat the brain disease that has harmed her memory, her speech and her senses.

Patient advocates have hailed the decision this week of state medicines buyer Pharmac to at last fund a drug to treat Alzheimer's - more than a decade after it became available.

Pharmac waited until one of the original drugs, containing donepezil, came off patent and a generic version was offered at a greatly reduced price.

It expects the generic Donepezil-Rex will be available from early July, and that 15,000 patients will be using it for Alzheimer's or related forms of dementia within three years.

Until now, many have chosen to pay $150 to $300 a month themselves for donepezil or similar drugs in the hope of delaying the progression of the brain-damaging disease.

Ms Cameron, 63, of Christchurch, paid $240 a month for galantamine - which, like donepezil, is in the group called acetylcholinesterase inhibitors - until she could no longer afford it.

She noticed problems in 2002 and was diagnosed with Alzheimer's in 2005. At first she lost her senses of smell and taste and her speech and memory deteriorated.

The senses improved a little and her speech is now fine except when she is stressed. But her memory remains a problem, and she has had to devise strategies to handle problem areas.

"I only use the range when someone else is in the house with me so I remember to turn it off."

Ms Cameron, who is proud to be still living in her own home, is uncertain whether to credit galantamine with holding her condition in check or whether that would have happened anyway.

Regardless, she plans to make an early visit to her doctor for a Donepezil-Rex prescription once Pharmac confirms the funding.

Donepezil has been shown to slow Alzheimer's symptoms, improve cognition and slow the decline of overall function.

It is also associated with enabling people to live longer in their own homes.

More than 40,000 people in New Zealand are believed to have dementia. More than half have Alzheimer's.

Alzheimer's New Zealand national director Johan Voss said the funding would make a big change to patients' lives.

"We have advocated for over 10 years to make this happen."

Pharmac said although donepezil and related drugs could slow disease progression, they did not work in all patients, and it was hard to identify beforehand who might benefit.

Because the generic drug was so much cheaper Pharmac could make it available to all patients with Alzheimer's or related forms of dementia, even though it wouldn't benefit all of them.