Niacin flush is a common side effect of taking high doses of supplemental niacin, which treats cholesterol problems. While harmless, its symptoms — skin that’s red, warm, and itchy — can be uncomfortable.
The symptoms of niacin flush can make people stop taking niacin (1). The good news is that you can reduce your likelihood of getting niacin flush.
This article describes what you need to know about niacin flush, including:
- what it is
- what causes it
- what you can do about it
What is niacin flush?
Niacin flush is a common side effect of taking high doses of niacin supplements. It’s uncomfortable, but it’s harmless.
It appears as a flush of red on the skin, which may be accompanied by an itching or burning sensation (1).
Niacin is also known as vitamin B3. It’s part of the B complex of vitamins that play an essential role in turning food into energy for the body (2).
As a supplement, niacin is primarily used to treat high cholesterol levels. Nicotinic acid is the supplement form people usually use for this purpose.
The other supplemental form, niacinamide, doesn’t produce flushing. However, this form isn’t effective at altering blood fats, such as cholesterol (3).
There are two main forms of nicotinic acid supplements:
- immediate release, where the whole dose is absorbed at once
- extended release, which has a special coating that makes it dissolve more slowly
Niacin flush is a very common side effect of taking the immediate-release form of nicotinic acid. It’s so common that at least half of people who take high doses of immediate-release niacin supplements experience it (4, 5).
High doses of nicotinic acid trigger a response that causes your capillaries to expand, which increases the flow of blood to the skin’s surface (1, 6, 7, 8).
By some reports, virtually every person who takes high doses of nicotinic acid experiences flush (6).
Other medications, including some antidepressants and hormone replacement therapies (HRTs), can also trigger flush (1).
SUMMARYNiacin flush is a common reaction to high doses of niacin. It happens when capillaries expand, increasing blood flow to the skin’s surface.
Symptoms of niacin flush
When niacin flush occurs, symptoms typically set in about 15–30 minutes after taking the supplement and taper off after about an hour.
The symptoms mainly affect the face and upper body, and include (9, 10):
- Reddening of the skin. It can appear as a mild flush or be red like a sunburn.
- Tingling, burning, or itching. This can feel uncomfortable or even painful (9).
- Skin that’s warm to the touch. As is the case with sunburn, skin may feel warm or hot to the touch (11).
People generally develop a tolerance to high-dose niacin. So even if you experience niacin flush when you first start taking it, that will probably stop in time (1, 8).
SUMMARYNiacin flush can appear and feel much like a sunburn. However, symptoms typically go away after an hour. People usually develop a tolerance to the supplements over time.
Why people take large doses of niacin
Doctors have long prescribed high doses of niacin to help people improve their cholesterol levels and prevent heart disease (5).
Taking high doses of niacin has been shown to produce the following improvements in blood cholesterol and lipids:
- Increase HDL (good) cholesterol. It prevents the breakdown of apolipoprotein A1, which is used to make HDL (good) cholesterol. It can increase HDL (good) cholesterol by up to 20–40% (1, 12).
- Reduce LDL (bad) cholesterol. Niacin speeds the breakdown of apolipoprotein B in LDL (bad) cholesterol, causing less to be released by the liver. It can reduce LDL (bad) cholesterol by 5–20% (11, 13, 14).
- Lower triglycerides. Niacin interferes with an enzyme that’s essential for making triglycerides. It can lower triglycerides in the blood by 20–50% (3, 11).
People only experience these positive effects on blood fats when they take therapeutic doses of niacin in the range of 1,000–2,000 mg per day (5).
To put that in perspective, the recommended daily intake for most men and women is 14–16 mg per day (9, 10).
Niacin treatment isn’t typically the first line of defense against cholesterol problems, since it can cause side effects other than flush.
However, it’s often prescribed for people whose cholesterol levels don’t respond to statins, which are the preferred treatment (15).
It’s also sometimes prescribed to accompany statin therapy (16, 17, 18, 19).
Niacin supplements should be treated like a drug and only taken under medical supervision, since they can have side effects.
SUMMARYHigh doses of niacin are typically used to improve cholesterol and triglyceride counts. They should only be taken under medical supervision, since they carry a risk of side effects.
Is it dangerous?
Niacin flush is harmless.
However, high doses of niacin can cause other, more dangerous side effects, although these are rare (20).
The most harmful of these is liver damage. High doses of niacin may also cause stomach cramping, so don’t take them if you have a stomach ulcer or active bleeding (9, 21, 22, 23, 24).
You also shouldn’t take high doses if you’re pregnant since it’s considered a category C drug, meaning at high doses, it could cause birth defects (22).
Interestingly, although the flush isn’t harmful, people often cite it as the reason they want to discontinue their treatment (1).
And that in itself can be a problem, since if you don’t take niacin as it’s prescribed, it’s not at all effective at preventing heart disease.
According to reports, 5–20% of people who have been prescribed niacin stop using it because of flush (5).
If you’re experiencing niacin flush, or are concerned about it as a possible side effect of these supplements, tell your healthcare provider. They can help you figure out how to reduce the chances of flush or discuss alternative treatments.
Also, because there are other, more harmful side effects associated with taking these supplements, do not try self-medicating with niacin.
SUMMARYNiacin flush is harmless. However, the supplements can have other harmful side effects, and certain people should not take them.
How to prevent niacin flush
Here are the main strategies people use to prevent niacin flush:
- Try a different formula. Roughly 50% of people taking immediate-release niacin experience flushing, but extended-release niacin is less likely to cause it. And even when it does, symptoms are less severe and don’t last as long (1, 4, 11). However, extended-release forms may carry a greater risk of liver damage.
- Take aspirin. Taking 325 mg of aspirin 30 minutes before the niacin can help reduce the risk of flush. Antihistamines and nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, can also minimize the risk (5, 10, 25, 26).
- Ease into it. Some experts recommend starting with a smaller dose like 500 mg and then increasing to 1,000 mg gradually over the course of 2 months, before finally increasing to 2,000 mg. This strategy could bypass flush entirely (5).
- Have a snack. Try taking niacin with meals or with a low-fat evening snack (5).
- Eat an apple. Some early research suggests that eating an apple or applesauce prior to taking niacin may have a similar effect to aspirin. Pectin in apple seems to be responsible for the protective effect (10).
Taking aspirin, eating a snack, slowly increasing the dosage, or switching formulas may help you prevent niacin flush.
Differences between forms of niacin
As mentioned above, to avoid unwanted symptoms, including flushing, some people opt for extended-release or long-acting niacin.
However, extended-release and long-acting niacin differ from immediate-release niacin and may cause different health effects.
Long-acting niacin is associated with significantly reduced flushing, as it’s absorbed over a long time period that typically exceeds 12 hours. Because of this, taking long-acting niacin significantly reduced the chances of flushing (11).
However, because of the way the body breaks it down, taking long-acting niacin may have toxic effects on the liver, dependent on the dose taken (11).
Although uncommon, switching from an immediate-release niacin to a long-acting niacin or significantly increasing your dose can result in serious liver damage (27).
What’s more, niacin absorbability depends on the niacin supplement that you take.
For example, the body absorbs nearly 100% of nicotinic acid, which raises niacin blood levels to an optimal range in about 30 minutes.
In contrast, inositol hexanicotinate (IHN), a “no-flush” niacin, isn’t absorbed as well as nicotinic aid (28).
Its absorption rate varies widely, with an average of 70% being absorbed into the bloodstream.
Plus, IHN is significantly less effective than nicotinic acid at increasing serum niacin. IHN usually takes between 6-12 hours to raise blood levels of niacin to near the optimal range (28).
Some studies suggest that peak niacin blood levels can be over 100 times greater when supplementing with nicotinic acid compared to supplementing with IHN.
Research also shows that IHN has minimal effect on blood lipid levels (28).
Because absorbability can significantly vary depending on the form of niacin used, it’s a good idea to ask your healthcare provider what form would be best for your specific health needs.
summaryAbsorbability differs between forms of niacin. Some types of niacin are more effective at raising blood levels than others.
The bottom line
Niacin flush can be an alarming and uncomfortable experience.
However, it’s actually a harmless side effect of high-dose niacin therapy. What’s more, it may be preventable.
That said, large doses of niacin can have other, more harmful side effects.
If you want to take high doses of niacin for health reasons, make sure to do so under medical supervision.