Three key drugs to treat memory loss associated with Alzheimer's disease could be withdrawn after an assessment by the NHS treatment advisory body.
The drugs were originally recommended for use four years ago
The National Institute for Clinical Excellence has put forward the draft guidance after assessing the clinical and cost effectiveness of the drugs.
A final decision on using donepezil, rivastigmine and galantamine in England and Wales will be made in July.
Patients already taking the drugs would not have them withdrawn, Nice said.
The guidance does not mean the drugs do not work or are harmful, just that the cost to the NHS does not warrant the benefits gained from patients taking them.
The drugs, which campaigners estimate cost £2.50 per day per patient, improve memory and can make daily living tasks easier.
Campaigners and medical experts condemned the move, which reverses previous Nice guidance in 2001 that said the drugs should be used as standard.
Alzheimer's Society chief executive Neil Hunt said: "We are stunned at the proposal that vulnerable people with Alzheimer's disease should not receive treatments that have been proven to work.
"If these initial recommendations are finally approved, thousands of people with dementia will be denied the only drug treatment available to them.
"This seems just another example of the NHS failing to take dementia seriously as a medical condition.
"Despite the fact that these drugs are proven to work, Nice believes that they aren't good value for money. We know they are."
And Professor Simon Lovestone, of the Alzheimer's Research Trust, said it was "appalling" to deny the treatment to patients.
"While the drugs do not help everyone, many carers and families have told us they have been a huge help."
Professor Susan Benbow, of the Royal College of Psychiatrists, said while they did not cure the disease the drugs brought "substantial benefits".
"On average, drugs for Alzheimer's disease delay the decline associated with the illness by six to nine months.
"This is a degree of benefit which clinicians, patients and carers value.
"In our opinion, this degree of improvement in a devastating and progressive illness for which no other treatments are available is well worth the modest costs of the drugs."
She said if the drugs were withdrawn, the alternatives would include anti-psychotic drugs which carry side effects.
The Association of the British Pharmaceutical Industry (ABPI) said that if the drugs were withdrawn it would act as a significant deterrent to companies undertaking further research in this area.
Dr Richard Barker, ABPI director general, said: "NICE's draft recommendations put small cost savings before the benefit that these medicines can bring to so many people who have Alzheimer¿s - and to their family, friends and carers.
"It also sends a discouraging message to pharmaceutical companies that are putting major research work into discovering new, innovative medicines to help people with Alzheimer's and other forms of dementia.
"How can companies justify investing huge sums in research and development - it costs on average about £550m to develop a new medicine - if such decisions can be made to withhold medicines from patients despite their benefits?"
Nice said it was only draft guidance at present and patients would not be affected until the final decision in July when the consultation had been finished.
Meanwhile, a fourth drug, memantine, which is used to treat moderate to severe Alzheimer's could also be withdrawn, Nice said.
However, the drug will continue to be available for clinical trials under the proposals.