The government has announced plans for people to be able to make a "living will".
The scheme will allow people diagnosed with early forms of diseases such as Alzheimer's to make wills detailing their preferences regarding medical care.
If the 2004 Mental Capacity Act's Code of Practice comes in to being, the will maker would be able to give "lasting powers of attorney" to a family member or friend.
Previously, living wills could only deal with financial matters.
Health minister Rosie Winterton said the Mental Capacity Act is "an important step towards empowering vulnerable people who lack mental capacity to make decisions for themselves.
"The Code of Practice will ensure that best practice is followed and strict safeguards are in place to protect these most vulnerable people," she added.
The announcement has drawn criticism from some quarters, with fears that the legalising of euthanasia will be the inevitable end result of the changes.
The code is now to undergo a period of consultation until July.