Some cholesterol lowering drugs (statins), when taken with grapefruit juice, can raise the patient's risk of muscle toxicity, says the UK Medicines and Healthcare Products Regulatory Agency (MHRA). The MHRA said this was particularly so with Zocor (simvastatin) from Merck & Co and Lipitor from Pfizer. There is a liver enzyme important for drug metabolism. Grapefruit juice restrains the activity of this enzyme. If one drinks grapefruit juice regularly, there is a risk that he or she will have raised levels of the statin in his or her bloodstream.