More than 2.4million people will lose access to free prescriptions if the government goes ahead with plans to raise the benefit in line with the state pension age.
It would be "a kick in the teeth" for both older people and the NHS, a charity said, and could lead to people skipping vital medication to avoid the costs of treatment.
Currently people qualify for free prescriptions - which cost £9.35 per medicine - at 60.
However, last month the Government launched a consultation on raising the age to 66 to tie in with the state pension age.
The Department of Health wants to bring the free prescription age in line with the state pension age - which is currently 66.
It is estimated the move could bring in £300million for the NHS by 2026/27.

If given the go ahead, it would mean 2.4million older people will lose their right to free prescriptions in England.
Those on low incomes just above the benefits line are likely to be worst hit, with thousands forced to ration their medication because they cannot afford the extra cost, Age UK said.
It added scrapping free prescriptions for this age group is 'likely to exacerbate existing health inequalities' and have a 'devastating impact' on older people's health and put further pressure on the NHS.

Jan Shortt, National Pensioners Convention general secretary, said: "This will have a massive negative effect on the health of pensioners who lose their free prescriptions.
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"Prescription charges are not affordable if you are on low income without financial help of some kind.”
Age UK has launched a Save Free Prescriptions campaign ahead of the consultation’s closure in just over two weeks' time.
Caroline Abrahams, Age UK's charity director, said: “This proposed policy is a kick in the teeth, both for poorly older people and the NHS.
"It is also extremely illjudged because the money the Government will save will almost certainly be outweighed by the additional costs to the NHS, if people fail to take their medication because they can't afford it and become ill.”
A health department spokesman said the age people received free prescriptions in England had not changed since 1974 for women, and 1995 for men.
He added: “We continue to protect the most vulnerable and support is available for those on a low income and on certain benefits.”