NICE aforesaid that Aricept, which costs about �2.50 a day, did not make enough of a difference to advocate it for all patients and so was not good economic value for money.
Pratchett acknowledges that through his success as an writer - his Discworld series has sold 55 million books universal - he is well able to afford to Aricept.
But he is interested for other people with Alzheimer's wHO lack his means.
"I feel particularly angry on behalf of early-onset patients because it feels like an insult and the younger you are the more than insulting it is," he says.
"A lot of hoi polloi with early onset have got dependants both younger and older and they're trying to hold down a job.
"It is a really nasty disease and I cannot imagine cancer patients organism denied a drug like this in similar fate," Pratchett added.
Fear factor
He says that he has noticed a huge change in his circumstance since he started pickings Aricept.
"If I'm not on the drug I'd find certain things difficult, doing up buttons so you get a line of buttons in the shirt done up right toilet be a problem," he said.
Alzheimer's chiefly affects older people
"In theory I should be that much worse, but my wife has said that I'm better now than I was in the autumn."
But Pratchett says that the advantages of pickings the drug are wider than that.
"Alzheimer's scares people and at four o'clock in the morning it scares me, and Aricept is well worth having for the relief that it brings."
He said that the decisiveness not to give it to early stage sufferers, but to provide dislodge treatment for obesity and sexual powerlessness, indicated the NHS "priorities are non right".
And the author as well told Panorama that he thought it was possible that NICE's decision was in part shaped by the fact that Alzheimer's was a disease preponderantly affecting older people, world Health Organization he aforesaid were cerebration of as "a softer target".
Panorama: The Postcode Lottery: It Could Be You will be on BBC One at 8.30pm on Monday 18 August.
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