HDL cholesterol is increased by Merck's potential blockbuster in anacetrapib, which is an experimental cholesterol drug despite lowering LDL cholesterol.

John Boris, an analyst at Citigroup, told investors that it has been estimated that every year the drug could potentially have sales of more than $1 billion.

Merck however added that it will only be clear in 2015 that anacetrapib actually protects the heart by reducing heart attacks and other cardiovascular problems so cardiologists, patients and investors will have to wait.

An enzyme called CETP, which is involved in transforming particles of good cholesterol into bad cholesterol, is inhibited by Anacetrapib and this is how it works.

Patients in a group taking anacetrapib had a 39.8 percent reduction in bad cholesterol beyond that seen in the placebo group was experienced by 1,623 patients who were already taking statins to control their cholesterol.

More strikingly, there was an increase in good cholesterol by 138.1 per cent in the anacetrapib group.

Dr Luciano Rossetti, the head of global scientific strategy at Merck Research Laboratories said, "But the real impact of anacetrapib on heart health will not be known until researchers conduct a much larger study looking into whether the drug can reduce the risk of heart attacks, coronary deaths and other heart problems."