In "305 randomised controlled trials involving 339,274 individuals... no statistically detectable differences between exercise and drug interventions for secondary prevention of heart disease and prevention of diabetes." 

"Among stroke patients, exercise was more effective than drug treatment,..."

"...based on the available data, physical activity is potentially as effective as many drug interventions -- and call for more trials to address the disparity between exercise and drug-based treatment evidence."

Exercise 'Potentially as Effective' as Many Drugs for Common Diseases - http://www.sciencedaily.com/releases/2013/10/131001192009.htm