Another one of the more serious Winstrol side effects involves changes to cholesterol levels. Winstrol has the ability to increase LDL or bad cholesterol levels, while at the same time reducing HDL or good cholesterol levels. As such, those who already have high levels of LDL cholesterol in their bloodstream should forego taking it. Anyone who has a family history of high LDL cholesterol should have regular blood tests to check cholesterol levels while taking it. Patients who are already taking medication to control their cholesterol levels should avoid taking it altogether.
Winstrol in particular is known for exhibiting some profound negative cholesterol changes in humans as evidenced by some clinical studies. Winstrol administered orally at just 6mg daily for a 6 week period resulted in a reduction of HDL by 33%, alongside an LDL increase of 29% (all test subjects were healthy males engaged in regular physical exercise)  . Even the injectable Winstrol preparation has demonstrated to produce negative cholesterol profile changes. Only a single 50mg dose of injectable Winstrol was administered to 12 healthy test subjects, and resulted in significant HDL reduction with an increase in LDL (these negative cholesterol changes remained for a 4 week period following administration before returning to normal values)  .