A decision by the government's health watchdog to deny Alzheimer's drugs to patients with mild-stage disease is being challenged at the High Court.
Protesters gathered outside the court
The National Institute for Health and Clinical Excellence (NICE) ruled the medicines - donepezil, rivastigmine and galantamine - were not cost effective.
But critics argue the decision process was flawed and did not take into account the benefits to carers.
It is the first time a judicial review has been sought on a NICE decision.
The court heard from Lillian Turner, whose husband Keith has Alzheimer's.
In a written submission she said: "I find it abhorrent and disgusting that NICE is suggesting in its defence that a wife like me would be better resigning herself to the fact her husband may well end up in care, and would be well served by an NHS that withheld effective treatment so that day would dawn sooner than it otherwise should."
Drugs company Eisai brought the case to the High Court with support from fellow drugs firm Pfizer and the Alzheimer's Society.
David Pannick QC, representing the firm, told the court the NICE decision was procedurally flawed and irrational.
He said: "We are asking the court to conclude that NICE and its appeal panel failed properly to assess the issues and so the matter must go back for reconsideration."
NICE guidance in 2001 recommended the drugs - which can make it easier to carry out everyday tasks - should be used as standard.
But guidance published in November 2006, after months of appeals, stated that the drugs should only be prescribed to people with moderate-stage disease.
NICE's analysis of the evidence showed the drugs, which cost about £2.50 a day, did not make enough of a difference to recommend them for all patients and were not good value for money.
Campaigners are angry that people suffering from Alzheimer's have to get worse before they are eligible for treatment.
They argue that NICE did not properly evaluate the impact of the drugs on the quality of life of carers and that the figures on the cost of long-term care used in their analysis were too low.
In addition, they say the test used to determine the severity of a patient's Alzheimer's discriminates against people who do not speak English as their first language or those with learning difficulties.
About 700,000 people in the UK have a form of dementia and more than half of those have Alzheimer's disease.
The outcome of the four-day hearing will have an impact on the whole of the UK as regulators in Scotland and Northern Ireland are waiting for the result before making a decision.
Neil Hunt, chief executive of the Alzheimer's Society, said: "People with Alzheimer's disease and their carers have fought long and hard for their day in court.
"These treatments have benefited so many families already - where is the justice in NICE's decision to snatch them away?
"We have to fight NICE's fatally flawed process, which has failed to recognise the benefits these treatments have for carers."
A spokesperson for Pfizer said: "We believe the process was flawed.
"They are asking clinicians to say to their patients 'you have to get worse and then we can treat you'."
Andrew Dillon, chief executive of NICE, said: "Our consultation, decision-making and appeals processes are transparent and fair.
"The recommendations on the use of drugs for treating Alzheimer's disease were developed over a three-year period in which careful analysis and detailed discussions with patient groups, doctors and the drug manufacturers demonstrated our commitment to involving those whom our decisions affect.
"The reality is that, for Alzheimer's disease, drugs are only part of the care that needs to be offered.
"Non-drug interventions have an important part to play and the evidence indicates that drugs are simply not effective for some patients."