Exercise may be just as effective as drugs at treating common diseases, according to a large study.
The research, on more than 339,000 people, found being active was just as good as medicine for those with existing heart disease and in the prevention of diabetes.
It also appeared to be a more effective treatment than drugs for people who had suffered a stroke.
Experts at the London School of Economics, Harvard Medical School and Stanford University School of Medicine in the United States examined the findings of 305 trials on four conditions: pre-diabetes, heart disease, stroke and heart failure.
Of the studies, 57 looked specifically at the effect of exercise and included 14,716 people.
More than 200 trials examined drug treatment for the conditions, such as the effects of statins, beta blockers and anti-platelet therapy on preventing significant illness in those with heart disease.
The results showed that exercise was just as effective as drugs in treating people with heart disease and whose blood sugar control suggested they were at high risk of diabetes.
The results on heart failure were more unclear, with diuretic drugs being found to be more effective than exercise and all other types of drug treatment.
The findings were most impressive for stroke, with exercise found to be more beneficial than drug treatment.
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Writing online in the British Medical Journal (BMJ), the team concluded: "Our analysis suggests that exercise potentially had similar effectiveness to drug interventions with two exceptions.
"In the case of stroke rehabilitation, exercise seemed to be more effective than drug interventions.
"In heart failure, diuretics outperformed all comparators, including exercise."
The experts said their findings suggest "exercise interventions should therefore be considered as a viable alternative to, or alongside, drug therapy.
"Indeed, an increasing number of experts recommend prescribing an 'exercise pill' as a preventive strategy to reduce morbidity and mortality."
Drug regulators should also consider forcing pharmaceutical companies to compare drugs with exercise rather than just a placebo.
"In cases where drug options provide only modest benefit, patients deserve to understand the relative impact that physical activity might have on their condition," they added.
The team said in the UK only 14% of adults exercise regularly at a time when prescription drug use has risen sharply.
An average of 17.7 prescriptions for every person were dispensed in England in 2010, compared with 11.2 in 2000.
The authors point out that the amount of trial evidence on the mortality benefits of exercise is considerably smaller than that on drugs, and this may have had an impact on their results.
Amy Thompson, senior cardiac nurse at the British Heart Foundation, said: "An active lifestyle brings many health benefits.
These researchers suggest doctors should think more about prescribing exercise to ward off heart disease and stroke.
"However, there is limited evidence comparing the effect of exercise to that of drugs. Further research is needed to contrast the two treatments before we can draw any firm conclusions.
"Medicines are an extremely important part of the treatment of many heart conditions and people on prescribed drugs should keep taking their vital meds.
"If you have a heart condition or have been told you're at high risk of heart disease, talk to your doctor about the role that exercise can play in your treatment."
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Dr Peter Coleman, deputy director of research at the Stroke Association, said: "We know that exercise, as well as intensive physiotherapy, can have a vital role in helping patients recover after a stroke.
"Moderate physical activity for example can reduce the risk of stroke by up to 27%. However, exercise alone should not be considered an alternative for patients taking prescribed medication, as advised by their GP.
"This study suggests that exercise could be beneficial in increasing life expectancy compared to blood-thinning drugs. We would like to see more research into the long-term benefits of exercise for stroke patients."
Dr Matthew Hobbs, head of research at Diabetes UK, said: "We already know that the best way to reduce your risk of developing Type 2 diabetes is to maintain a healthy weight by combining being regularly physically active with eating a healthy balanced diet.
"NHS guidelines for the prevention of Type 2 diabetes already reflect this, so these findings, which show that increased physical exercise is at least as good as drugs in preventing Type 2 diabetes, simply reinforce what should already happen in practice."