It is very important that your doctor check your progress at regular visits. This will allow your doctor to see if the medicine is working properly and to decide if you should continue to take it. Blood tests may be needed to check for unwanted effects.
Using this medicine while you are pregnant can harm your unborn baby. Use an effective form of birth control to keep from getting pregnant. If you think you have become pregnant while using the medicine, tell your doctor right away.
Do not use simvastatin if you are also taking any of the following medicines: boceprevir (Victrelis®), cyclosporine (Gengraf®, Neoral®, Sandimmune®), danazol (Danocrine®), gemfibrozil (Lopid®), nefazodone (Serzone®), telaprevir (Incivek®), certain antibiotics (such as clarithromycin, erythromycin, itraconazole, ketoconazole, posaconazole, telithromycin, voriconazole, Nizoral®), or medicines to treat HIV/AIDS (such as atazanavir, indinavir, nelfinavir, ritonavir, saquinavir, Crixivan®, Kaletra®, Lexiva®, Norvir®, Prezista®, Reyataz®). Using these medicines together with simvastatin may increase your risk of muscle injury and could result in kidney problems.
Chinese patients who are taking large amounts of niacin (greater than or equal to 1 gram or 1000 milligrams per day) together with this medicine may have an increased risk for muscle injury. Talk to your doctor if you are Chinese or have Chinese ancestry and take large amounts of niacin (Niacor®, Niaspan®). You may need a different dose of this medicine.
Call your doctor right away if you have unexplained muscle pain, tenderness, or weakness, especially if you also have unusual tiredness or a fever. These could be symptoms of serious muscle problems, such as myopathy or immune-mediated necrotizing myopathy (IMNM). Myopathy is more common when high doses of simvastatin (e.g., 80 milligrams) are used, but some people get myopathy with lower doses.
Call your doctor right away if you have dark-colored urine, diarrhea, a fever, muscle cramps or spasms, muscle pain or stiffness, or feel very tired or weak. These could be symptoms of a serious muscle problem called rhabdomyolysis, which can cause kidney problems.
Call your doctor right away if you get a headache, stomach pain, vomiting, dark-colored urine, loss of appetite, weight loss, general feeling of tiredness or weakness, light-colored stools, upper right stomach pain, or yellow eyes or skin. These could be symptoms of liver damage.
Make sure any doctor or dentist who treats you knows that you are using this medicine. You may need to stop using this medicine if you have major surgery, a major injury, or you develop other serious health problems.
Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.