Doctors are encouraged to discuss end of life wishes early
The medical regulator is to issue updated guidance to doctors on making treatment decisions at the end of life.
Doctors must consider any harm caused by going against patient wishes in withdrawing artificial nutrition, the General Medical Council says.
The draft recommendations also advise on holding early discussions with patients about end of life decisions.
Doctors at the British Medical Association said any "additional clarification" is welcome.
The guidance, which will be put out for consultation, builds on a raft of previous reports on how doctors should approach end of life care.
It has long been the case that patients have a legal right to refuse treatment.
But in recent years there has been controversy about the right of patients to be tube fed or hydrated right up until the point of death.
In 2005, Leslie Burke, 45, who has a degenerative brain condition, lost his legal case to prevent doctors withdrawing artificial nutrition against his wishes.
The GMC guidance states that in some cases providing nutrition or hydration at the end of life may cause unnecessary suffering.
For example, if a patient's kidneys were not functioning or fluid was collecting in their lungs then to continue a saline drip might cause a more unpleasant death.
Doctors can still withdraw treatment in the best interests of the patient but the new guidance says they "must consider any harm that might be caused" in going against the patient's interests.
The recommendations also provide clarification on when attempts at resuscitation with CPR may or may not be in a patient's best interests.
It does not cover assisted suicide, which is illegal in the UK.
Jane O'Brien, GMC assistant director of standards and fitness to practise, said: "Clinicians still have the final say on 'best interests', but we are asking them to give greater weight to patients' wishes in a more formal sense than we have before.
"Those who have strong feelings about how they want themselves or their loved ones to be treated should expect those feelings to be considered."
Dr Vivienne Nathanson, head of science and ethics at the British Medical Association, said the advice provides "a good steer" for doctors on how to approach the difficult area of end of life care.
"The BMA already provides guidance on this matter and believes that the patients' advance wishes and their families' views must be taken into account when clinical decisions are made in regard to end of life treatments.
"It is essential that doctors and patients talk together about the best way forward in these circumstances.
"We believe that doctors already follow this advice, but additional clarification is always welcome."