All drugs can have side effects, and what suits one person won't another.
Have another word with your doctor, and explain exactly what you've done, and why.
As the name suggests, this drug is a statin, and lowers cholosterol levels, therefore helping to prevent heart disease, but there can be side effects with it, and it should never be taken if you consume grapefruit or grapefruit derivatives.
It can be taken in doses of up to 80mg, but this's proved to be toxic, and can effect the kidneys. As a general bit of information, perhaps this might help:
http://en.wikipedia.org/wiki/Simvastatin