A decision not to continue funding antidementia drugs on the NHS for some Alzheimer's disease patients is facing a legal challenge in the High Court.
Drug companies supported by the Alzheimer's Society are contesting the rulings made by the National Institute for Health and Clinical Excellence (NICE).
NICE says it made its recommendations because the drug treatments are not particularly effective for people with mild Alzheimer's disease, and resources should be put into other medicines available on the NHS.
The four-day case before Mrs Justice Dobbs at London's High Court centres on the use of acetylcholinesterase inhibitors (AChEIs) in the treatment of Alzheimer's disease.
NICE recommends that three anticholinesterase drugs - Aricept (donepezil), Exelon (rivastigmine) and Reminyl (galantamine) should not be prescribed for patients in the early stages of the disease.
But drug manufacturers Eisai and Pfizer argue the appraisal process was unfair.
The Alzheimer's Society has said it believes the process used by NICE to reach its decision is "fundamentally flawed".
Neil Hunt, the society's chief executive, said: "Another 100,000 people will develop dementia this year alone and the result of this case will affect not only them but their families too.
"We have to fight NICE's fatally flawed process, which has failed to recognise the benefits these treatments have for carers."