Short answer: It can amount to taking extra statin. NCCIH says red yeast rice can contain monacolin K, which is chemically identical to the statin lovastatin, and that products with meaningful amounts can have the same side effects and drug interactions as statins, including muscle, kidney and liver damage. A test of 28 US brands found monacolin K varied more than 60-fold, and none listed the amount. Ask your prescriber before combining them.
NCCIH explains that red yeast rice is rice fermented with a mold, usually Monascus purpureus, which can enrich it with substances called monacolins. Monacolin K is structurally identical to lovastatin, a prescription statin that slows the body's production of cholesterol.
How much is in a product is unpredictable. In a 2017 analysis of 28 brands from mainstream US retailers, monacolin K was not detected in 2, and in the other 26 it ranged from 0.09 to 5.48 mg per 1,200 mg of red yeast rice. At the makers' suggested daily servings, intake would range from 0.09 to 10.94 mg a day, more than 120-fold. None of the 28 labels listed the amount.
NCCIH says red yeast rice products with significant monacolin K can have the same potential side effects as statin drugs, including muscle, kidney and liver damage, and can have the same types of drug interactions, so they may interfere with certain medicines or raise the chance of side effects.
Someone already on a statin who adds red yeast rice may be adding more of a statin-like drug on top of the prescribed dose, in an amount neither they nor their prescriber can know from the label. The FDA grapefruit page makes a related point about statins: too much statin in the body raises the risk of liver and muscle damage that can lead to kidney failure.
NCCIH says that, according to the FDA, red yeast rice products with enhanced or added lovastatin cannot be sold as dietary supplements in the US, because lovastatin was approved as a drug first. Products with considerable monacolin K are considered unapproved new drugs. The FDA has sent warning letters to companies selling such products. Products with very little monacolin K may not lower cholesterol at all.
NCCIH also flags a contaminant, citrinin, which can damage the kidneys. In a 2021 analysis of 37 products, only one had citrinin below the European Union limit, and four products labeled "citrinin-free" were contaminated. It says red yeast rice is not recommended during pregnancy or breastfeeding.
If you use red yeast rice or are thinking of switching between it and a prescribed statin, your prescriber can weigh it against your lipid results. Worth bringing: the product name, dose, start date, any muscle aches or dark urine, and your latest lipid panel. Dose Track stores supplements, medicines and lab results together.
Read more on Dose Track: Red yeast rice guide · Cholesterol · Lipid panel (glossary) · Bergamot · Plant sterols