More than a third of elderly patients who are dying receive "invasive and potentially harmful" treatments in their last weeks of life, according to the biggest review of its kind.
Analysis of data from 1.2 million patients worldwide, including from England, found patients being subjected to "excessive" and unnecessary treatments that make no difference to the course of their illness.
Researchers said families are part of the problem, with some struggling to accept that nothing more can be done for their loved ones, and expecting "heroic" interventions from doctors.
The review, led by experts at the University of New South Wales in Australia, involved 10 countries and also looked at the experiences of bereaved families and doctors.
Published in the International Journal for Quality in Health Care, it found around a third of elderly patients with advanced, irreversible conditions - such as cancer - were given treatments that were of no benefit to them.
This included a third of cancer patients given chemotherapy in the last six weeks of life, 10% of all patients admitted to intensive care, 33% given antibiotics, cardiovascular, digestive or endocrine medicines, and 30% given dialysis, radiotherapy, blood transfusions or other life support.
A quarter of patients who had Do Not Resuscitate (DNR) orders in their notes were resuscitated, while up to half of patients underwent invasive blood tests and scans.
Some also received intensive cardiac monitoring, but all these treatments made "little or no" difference to the outcome and might have prevented a comfortable death, researchers said.
Dr Magnolia Cardona-Morrell, who led the research at the university's Simpson Centre for Health Services Research, said big advances in medical technology have led to "unrealistic" expectations about what doctors can achieve.
She said: "It is not unusual for family members to refuse to accept the fact that their loved one is naturally dying of old age and its associated complications and so they pressure doctors to attempt heroic interventions.
"Doctors also struggle with the uncertainty of the duration of the dying trajectory and are torn by the ethical dilemma of delivering what they were trained to do, save lives, versus respecting the patient's right to die with dignity.
"Our findings indicate the persistent ambiguity or conflict about what treatment is deemed beneficial and a culture of 'doing everything possible.
"The lack of agreed definitions in the medical community of what constitutes 'treatment futility' also makes a global dialogue challenging."
She said non-beneficial treatments should be regarded as those which "prolong suffering rather than survival, that can potentially cause harm, and are sometimes given against patients' wishes".
She called for "honest and open" discussions with patients or their families as a way of avoiding treatments that would not help prolong life.
She added: "More training for doctors will help them let go of the fear of a wrong prognosis, because they will be better able to identify patients near the end of life.
"As a community we must also stop shying away from the topic of death. Start a discussion now with your elderly loves ones about their end of life care preferences before they become too ill to have that conversation."
The 38 studies included patients, bereaved relatives, doctors and nurses from the US, Canada, England, Australia, France, Holland, Brazil, Taiwan, South Korea and Israel.