National Center for Complementary and Integrative Health (NCCIH)
NIH…Turning Discovery Into Health

Información en Español

Health Topics A-Z

National Institutes of Health • National Center for Complementary and Integrative Health

NCCIH Clinical Digest

for health professionals

High Cholesterol and Complementary Health Practices:
What the Science Says

February 2013

Dietary Supplements

Red Yeast Rice

Strength of Evidence

  • Some red yeast rice products contain substantial amounts of monacolin K, which is chemically identical to the active ingredient in the cholesterol-lowering drug lovastatin. Available evidence on the cholesterol-lowering effects of red yeast rice has focused on these products.
  • Researchers have not reported results of any studies of red yeast rice products that contain little or no monacolin K, so whether these products have any effect on blood cholesterol is unknown.

Scientific Evidence

  • Red yeast rice products containing substantial amounts of monacolin K, which is chemically identical to the active ingredient in the cholesterol-lowering drug lovastatin, may lower blood cholesterol levels and can cause the same types of side effects and drug interactions as lovastatin. The U.S. Food and Drug Administration (FDA) has determined that red yeast rice products that contain more than trace amounts of monacolin K cannot be sold legally as dietary supplements.
  • Other red yeast rice products contain little or no monacolin K. It is not known whether these products have any effect on blood cholesterol levels.
  • Consumers have no way of knowing how much monacolin K is actually present in most red yeast rice products. The labels on these products usually state only the amount of red yeast rice that they contain, not the amount of monacolin K.
  • Given safety concerns and the lack of evidence for legally marketed products, red yeast rice supplements should not be used as a treatment for high cholesterol.


  • The same types of side effects that can occur in patients taking the drug lovastatin can also occur in patients who take red yeast rice products that contain monacolin K. Potential side effects include myopathy (muscle symptoms such as pain and weakness), rhabdomyolysis (a condition in which muscle fibers break down, releasing substances into the bloodstream that can harm the kidneys), and liver toxicity. Each of these three side effects has been reported in people who were taking red yeast rice. Patients who take a prescription statin are routinely monitored by health care providers for these developing signs of toxicity, but those who take red yeast rice supplements often do so on their own, without such monitoring.
  • Red yeast rice supplements should not be used while pregnant or breastfeeding.
  • It is known that lovastatin can interact with a variety of drugs to increase the risk of rhabdomyolysis; these drugs include other cholesterol-lowering agents, certain antibiotics, the antidepressant nefazodone, drugs used to treat fungal infections, and drugs used to treat HIV infection. It is likely that red yeast rice products containing monacolin K could interact with these or other drugs in the same way.
  • If the process of culturing red yeast rice is not carefully controlled, a substance called citrinin can form. Citrinin has been shown to cause kidney failure in experimental animals and genetic damage in human cells. In a 2011 analysis of red yeast rice products sold as dietary supplements, 4 of 11 products were found to contain this contaminant.

Flaxseed and Flaxseed Oil

Strength of Evidence

  • Much research has been conducted on various preparations of flaxseed, flaxseed oil, and flaxseed lignans (which are present in high concentrations in flaxseed) for reducing cholesterol levels.

Scientific Evidence

  • Studies of flaxseed preparations to lower cholesterol levels report mixed results. A 2009 review of 28 clinical studies concluded that there was evidence of modest cholesterol-lowering effects for flaxseed and flaxseed lignans preparations. The effects were more apparent in postmenopausal women and in people with high initial cholesterol concentrations. There was no evidence of significant effects with flaxseed oil.
  • Some studies suggest that alpha-linolenic acid (a substance found in flaxseed and flaxseed oil) may benefit people with heart disease. But not enough reliable data are available to determine whether flaxseed is effective for heart conditions.


  • Flaxseed and flaxseed oil supplements seem to be well tolerated. Few side effects have been reported.
  • Flaxseed, like any supplemental fiber source, should be taken with plenty of water; otherwise, it could worsen constipation or, in rare cases, even cause intestinal blockage. Both flaxseed and flaxseed oil can cause loose stools or diarrhea.
  • In theory, the fiber in flaxseed (as with other supplemental fiber sources) may lower the body’s ability to absorb medications that are taken by mouth. Flaxseed should not be taken at the same time as any conventional oral medications or other dietary supplements.


Strength of Evidence

  • Much research has been conducted on the effects of various garlic supplements on blood cholesterol levels.

Scientific Evidence

  • Some evidence indicates that taking garlic supplements can slightly lower blood cholesterol levels; studies have shown positive effects for short-term (1 to 3 months) use. However, an NCCAM-funded study on the safety and effectiveness of three garlic preparations (fresh garlic, dried powdered garlic tablets, and aged garlic extract tablets) for lowering blood cholesterol levels found no effect.


  • Garlic supplements appear to be safe for most adults.
  • Side effects can include breath and body odor, heartburn, upset stomach, and rarely allergic reactions. These side effects are more common with raw garlic.
  • There is evidence that garlic supplements may thin the blood (reduce the ability of blood to clot) in a manner similar to aspirin. This effect may be a problem during or after surgery. Use garlic with caution if you are planning to have surgery or dental work, or if you have a bleeding disorder.
  • Garlic supplements have been found to interfere with the effectiveness of saquinavir, a drug used to treat HIV infection. Its effect on other drugs has not been well studied.

Other Dietary Supplements

  • There are not enough reliable data to determine whether green tea, noni, or red clover can aid in lowering blood cholesterol levels.
  • Research suggests that daily intake of soy protein may slightly lower levels of LDL (“bad”) cholesterol.

Healthy Behaviors


  • A diet low in saturated fat and trans fat has been shown to greatly affect blood cholesterol levels. In addition to conventional drug therapy, the National Heart, Lung and Blood Institute (NHLBI) at NIH recommends a “therapeutic lifestyle changes” program that includes a diet of:
    • Less than 7 percent of your daily calories from saturated fat
    • Less than 200 mg a day of cholesterol
    • 25 to 35 percent of daily calories from total fat (includes saturated fat calories)
    • Additional options to enhance lowering of LDL lowering include 2 grams/day of plant stanols or sterols and 1- to 25 grams/day of soluble fiber
    • Only enough calories to reach or maintain a healthy weight

Physical Activity

  • When the metabolic syndrome or associated high lipid risk factors (elevated triglyceride or low HDL cholesterol) are present, NHLBI’s clinical guidelines stress weight reduction and increased physical activity.
  • Regular physical activity has been shown help people manage their weight and, in that way, help raise HDL and lower LDL. NHLBI recommends 30 minutes of a moderate-intensity physical activity, such as brisk walking, on most days (if not all) of the week, with a goal of at least 150 minutes over the course of the week.

Weight Management

  • Losing extra weight has been shown to improve cholesterol and triglyceride levels and reduce risks of developing high blood pressure, diabetes, heart disease, and other serious health problems.
  • A body mass index (BMI) of 18.5-24.9 indicates a normal weight; a BMI of 25-29.9 is overweight; while a BMI of 30 or higher is obese.
  • A waist measurement of 35 inches or more for women or 40 inches or more for men is one of the factors involved in the metabolic syndrome and indicates an increased risk of obesity-related conditions, such as heart disease.

NCCIH Clinical Digest is a service of the National Center for Complementary and Integrative Health, NIH, DHHS. NCCIH Clinical Digest, a monthly e-newsletter, offers evidence-based information on complementary health approaches, including scientific literature searches, summaries of NCCIH-funded research, fact sheets for patients, and more.

The National Center for Complementary and Integrative Health is dedicated to exploring complementary health products and practices in the context of rigorous science, training complementary health researchers, and disseminating authoritative information to the public and professionals. For additional information, call NCCIH's Clearinghouse toll-free at 1-888-644-6226, or visit the NCCIH Web site at NCCIH is 1 of 27 institutes and centers at the National Institutes of Health, the Federal focal point for medical research in the United States.


Content is in the public domain and may be reprinted, except if marked as copyrighted (©). Please credit the National Center for Complementary and Integrative Health as the source. All copyrighted material is the property of its respective owners and may not be reprinted without their permission.

This page last modified November 20, 2018