Simvastatin is generally well-tolerated and side effects
are rare. Minor side effects
include constipation, diarrhea, fatigue, gas, heartburn, and headache. Major side effects include abdominal pain or cramps, blurred vision, dizziness, easy bruising or bleeding, itching, muscle pain or cramps, rash, and yellowing of the skin or eyes.
This could be an allergic reaction to the drug. It will stop if the drug is withdrawn.