Is Niacin Flush Harmful? Symptoms & Causes

Niacin flush occurs when you take doses of 1,000 mg or above of niacin or vitamin B3. Symptoms may include flushed skin or a prickly hot sensation on the face and upper body. The reaction usually starts 15-30 minutes after taking a relatively large dose.

Almost everyone experiences flushing with large doses of niacin. Although it may feel like an allergy, it is not a true allergic reaction. The reaction is common with over-the-counter immediate-release products because it is absorbed immediately by the body.

When you take high doses of niacin supplements, your capillary blood vessels dilate 800-fold in the subcutaneous region of the skin, causing flushing. This dilation occurs due to the release of a substance called prostaglandins. Usually, aspirin or acetylsalicylic acid can block the action of prostaglandins, thereby preventing flushing.

Symptoms of niacin flush may include:

• Reddening of the skin
• Burning
• Itching sensation
• Feelings of warmth

Call your doctor if you experience the following in addition to a niacin flush:

• Low blood pressure (which can increase the risk of falls)
• Extreme fatigue
• High blood sugar levels
• Nausea, heartburn, and abdominal pain
• Blurred or impaired vision and fluid buildup in the eyes

Long-term treatment with extended-release forms of nicotinic acid can cause liver problems such as:

• Hepatitis
• Liver failure

Niacin when taken as nicotinamide has fewer side effects than nicotinic acid. However, nicotinamide when taken more than 500 mg/day or more can cause the following:

• Diarrhea
• Easy bruising
• More bleeding
• Nausea
• Vomiting
• Liver damage

Some people take niacin supplements to combat the risk of heart diseases and atherosclerosis. Taking large doses of niacin daily can lower low-density lipoprotein (bad) cholesterol levels and improve high-density lipoprotein (good) cholesterol levels.

Although rare, long-term use of extended-release niacin tablets can cause harmful side effects such as liver damage. High doses of niacin are contraindicated in pregnant women due to the risk of congenital problems.

Niacin flushing is usually caused by over-the-counter immediate-release niacin supplements. Other types of niacin supplements include:

• Sustained-release niacin tablets: This type of supplement delivers the vitamin at a slower rate over many hours. They do not cause flushes, but long-term use of this supplement may cause liver damage in some people.
• Prescription extended-release niacin products: They release the drug at a slower rate but over a shorter period of time. Some of the advantages of this type of supplement include:
  • Less impact on the liver
  • Positive effects on cholesterol
  • Reduces flushing

Doctors generally prescribe large doses of niacin to improve cholesterol levels and prevent heart disease. High doses of niacin may have the following effects on blood cholesterol and lipids:

• Increase high-density lipoprotein (HDL; good) cholesterol levels: Niacin can increase HDL cholesterol levels by 20%-40%. HDL cholesterol is made from apoprotein A1. Limiting the breakdown of this protein can improve HDL cholesterol levels in the blood. Niacin prevents the breakdown of apoprotein A1, thereby improving HDL cholesterol levels.
• Reduce low-density lipoprotein (LDL; bad) cholesterol levels: Niacin reduces LDL cholesterol levels by 5%-20%. Apoprotein B is responsible for the generation of LDL cholesterol, and the substance promoting the breakdown of apoprotein B can lead to less release of LDL cholesterol from the liver. Niacin speeds up the breakdown of apolipoprotein B in LDL cholesterol.
• Lower triglycerides: Niacin can reduce triglycerides by 20%-50% because it interferes with an enzyme essential for making triglycerides.

To get these benefits, it is necessary to take niacin at a dose of 1,000 to 2,000 mg per day, which is much higher than the recommended daily intake for most people, which is 14-16 mg per day. 

Niacin is not the recommended treatment option for cholesterol due to the side effects, including flushing. However, physicians may prescribe niacin supplements if you fail to respond to statin therapy, which is the standard treatment for managing cholesterol. It is sometimes prescribed in adjunct to statin therapy.

Always consult your physician before taking any supplements to avoid any unwanted side effects.

To prevent niacin flushing, you can take the following measures:

• Start with a low dose of niacin and gradually increase the dose over weeks.
• Take the supplements with food to reduce the intensity.
• Take low-dose aspirin 30 minutes before the first dose of niacin.
• Eat apples or applesauce before taking the supplements to reduce the intensity of symptoms.
• Avoid the following after taking niacin supplements:
  • Spicy foods
  • Hot beverages or alcohol
  • Hot showers or baths