Labour is to announce a pledge to abolish prescription charges in England at its party conference next week.
Prescriptions are already free in Scotland, Wales and Northern Ireland.
In England the NHS charges £9 per item, and earned just over £575m from fees in 2017/18 - which the government has said is a valuable source of income.
More than 80% of prescriptions are already issued free of charge, as those on low incomes or with some long-term conditions are not required to pay.
People on benefits including Income Support, pregnant women, children and the over-60s are among those who do not pay.
There is also a list of "medical exemptions", including those who need to take insulin for type 1 and type 2 diabetes and people with an underactive thyroid.
But people with many other conditions - including overactive thyroid, asthma, chronic kidney disease and rheumatoid arthritis - are not on the list, which was drawn up in 1968.
Pre-payment certificates for those who do not qualify for free medication cost £104 per year.
Shadow health secretary Jonathan Ashworth, who will announce the policy at the Labour party conference in Brighton, said: "We know that the cost of prescriptions puts people off taking the medicine they need.
"Not only do people suffer illnesses and the effects of illnesses more than they need to but, in the long term, it costs the NHS more money because those people who don't take their medicines present with even more serious conditions later on."
'Unfair and outdated'
Kay Boycott, chief executive of Asthma UK, which has campaigned for people with the condition to get free prescriptions, welcomed Labour's announcement.
She said: "This could make a huge difference to help people with asthma stay well and reduce pressure on hard-pressed NHS services.
"We are urging the leaders of the main political parties to pledge to stop unfair and outdated prescription charges for people with asthma, and shall continue to press them until this change has been implemented."
Asthma UK and the Labour Party both highlighted the case of Holly Warboys, who died aged 19 after an asthma attack.
Her mum Cathy said: "Holly was on a low income and struggled to pay for her asthma prescription charges.
"She died suddenly from an asthma attack with just one puff left in her inhaler because she couldn't afford to buy another one."
"All of the political parties should pledge to scrap unfair asthma prescription costs and stand up for people like Holly."
Prof Helen Stokes-Lampard, chair of the Royal College of GPs, said: "We have always been supportive of any safe and sensible measures to reduce medication costs for patients and ensure access to necessary medication is equitable, so it's encouraging to have a renewed debate around a review of prescription charges.
"We fully appreciate the amount that prescription medications cost the NHS every year, and we would always encourage patients to buy over-the-counter or other widely available treatments where they can to help reduce this.
"But even though many of our most vulnerable patients are already exempt from standard prescription charges, the fact that fees exist in England means there is real risk that some people might not obtain and take the medication they need."