Shepherd's career interests were the investigation of factors responsible for the development of coronary artery disease and he was, in particular, interested in the role of heredity and the environment in the regulation of the levels of fats (like cholesterol) in the blood.
WOSCOPS, a randomized double-blind placebo-controlled trial that included 6595 men between the ages of 45 and 64 with elevated LDL-cholesterol levels, was based in Glasgow and reported its findings simultaneously at the Annual Conference of the American Heart Association and in the New England Journal of Medicine.
The study showed that treatment with pravastatin significantly reduced the risk of first-time heart attack and death in a sample of men with elevated cholesterol but no previous evidence of heart attack. Earlier meta-analyses had showed that pravastatin had the same effect with patients who had already experienced a heart attack but the WOSCOPS study paved the way to statins being used as a preventative measure.
In 2004 the UK became the first country in the world to have statins available without prescription.