10 Niacin Side Effects You Should Know About

Niacin (Niaspan, vitamin B3) is a naturally occurring B vitamin — but it’s not your ordinary supplement. Niacin comes in both over-the-counter (OTC) and prescription forms. And it’s FDA-approved to treat both high cholesterol and high triglyceride levels.

Even though niacin is a vitamin, there are still side effects to be aware of while taking it. Here’s what you should know.

Niacin side effects at a glance

Below are common and serious niacin side effects reported in clinical studies. Keep in mind, you may experience side effects not on this list. Or you may not experience any side effects at all. Your healthcare team can answer any questions or concerns you have while taking niacin.

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Common niacin side effects include:

• Flushing of the skin

• Diarrhea

• Nausea and vomiting

• Cough

• Itchy skin

• Rash

More serious niacin side effects include:

• New or worsening gout

• Blurry vision

• Low blood pressure

• Increased blood sugar (glucose)

• Increased risk of bleeding

• Muscle damage (if combined with statins)

• Liver problems

• Increased risk of heart attack and stroke

Let’s take a closer look at 10 niacin side effects and how to manage them.

1. Flushing

Flushing is the most common niacin side effect. It’s not dangerous, but it can be uncomfortable. Also known as the niacin flush, this side effect can make your skin feel itchy or warm. It commonly happens on the face, arms, or chest and typically lasts for about 30 minutes. You may also feel dizzy, have a fast heartbeat, or feel sweaty when flushing happens. Immediate-release niacin tends to cause more flushing than extended-release (ER) niacin.

Flushing often improves over time as your body adjusts to niacin. But you can help prevent it by taking 325 mg of aspirin at least 30 minutes before your niacin dose. Eating an apple along with niacin can also help. And it’s best to avoid alcohol and hot or spicy foods while taking niacin, as they can make flushing worse.

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In rare cases, flushing may be severe enough to cause fainting. This isn’t common, but if it happens be sure to let your prescriber know. You may need a lower niacin dosage or a different medication.

2. Diarrhea

Niacin can also cause diarrhea. Taking it with food can help. Starting with a low dose and gradually increasing it can also reduce the chance of this side effect.

Diarrhea should improve over time as your body adjusts to niacin. In the meantime, drink plenty of fluids to avoid dehydration. You can also try an OTC antidiarrheal, such as loperamide (Imodium A-D) or bismuth subsalicylate (Pepto-Bismol), if needed. But if your diarrhea is severe or doesn’t improve, talk to a healthcare professional for guidance.

3. Nausea and vomiting

Nausea and vomiting are common niacin side effects, especially with higher doses. As with diarrhea, taking niacin with a low-fat meal and gradually increasing the dosage can help. Eating smaller meals and avoiding spicy or greasy foods can also reduce nausea.

If you have a stomach ulcer or other gastrointestinal conditions, talk to a healthcare professional before taking niacin. It can worsen these conditions and may not be the best option for you.

4. Cough

Niacin can cause or worsen coughing for some people. It isn’t clear why this happens, but this side effect was more likely with a high niacin dose (2,000 mg per day). So lowering your dose may improve coughing if it occurs.

If you develop a cough that lasts for more than a week or two, talk to your prescriber. They can help determine if the cough is due to niacin or something else. From there, they can recommend the right treatment.

5. Itchy skin

Itchy skin is also a possible niacin side effect. This typically happens along with flushing, but it can also happen on its own.

As with flushing, itchy skin usually improves as your body gets used to niacin. Taking an extended-release formula and increasing your dose over time can also help. But if your itchy skin becomes bothersome, let your prescriber know.

Good to know: Itchy skin can also be a sign of an allergic reaction. If you also develop hives, have trouble breathing, or notice swelling of your mouth and throat after taking niacin, seek emergency care right away. 

6. Low blood pressure

It isn’t common, but niacin can cause low blood pressure (hypotension). This can lead to dizziness, lightheadedness, and weakness, especially when you move from sitting to standing.

Low blood pressure is more likely if you take too much niacin. But your risk is also higher if you take niacin with blood pressure medications, some antipsychotics, or certain erectile dysfunction (ED) medications. 

Share your medication list with your healthcare team before starting niacin to be sure it’s a safe option for you. And don’t take more niacin than recommended. If you’re experiencing low blood pressure symptoms while taking niacin, talk to your prescriber about other treatment options.

7. Increased blood sugar

Niacin can increase your blood sugar levels while you’re taking it, especially at doses over 1,000 mg per day. Because of this, niacin can also increase your risk of developing diabetes. If you’re already living with prediabetes or diabetes, niacin may affect your blood sugar control.

Your prescriber will likely keep an eye on your blood sugar levels while you’re taking niacin. Be sure to let them know if you notice symptoms of high blood sugar, such as:

• Feeling thirsty

• Peeing more than usual

• Having unexplained weight loss

If you test your blood sugar on your own, let your prescriber know if your levels are higher than usual while taking niacin.

8. Increased bleeding risk

Niacin can lower the number of platelets in your blood. Platelets play a key role in forming blood clots to stop bleeding. So lower platelet levels can increase your bleeding risk. This risk may be higher if you take niacin along with a blood thinner, such as warfarin (Coumadin) or apixaban (Eliquis).

Let your prescriber know if you have signs of minor bleeding, such as when brushing your teeth, or are bruising easier than usual. If you notice serious bleeding — such as blood in your urine or stool, a bruise that keeps getting bigger, or coughing up blood — seek emergency care right away.

9. Liver problems

Another rare but possible niacin side effect is liver problems. Because of this, niacin isn’t recommended if you’re already living with liver disease.

In most cases, niacin causes increased liver enzymes that resolve on their own. But more serious liver damage is possible. This seems to be more likely with high doses of extended-release niacin. It can also appear after switching from immediate-release niacin to an extended-release version.

If you notice signs of liver issues — such as nausea, stomach pain, and yellowing of the skin and eyes (jaundice) — seek medical care for guidance.

10. Increased risk of heart attack and stroke

Niacin supplements may actually increase your risk of heart attack and stroke over time. Since it also carries a risk for other serious side effects, most experts no longer recommend niacin for high cholesterol. The benefits simply don’t outweigh the risks when safer treatment options are available. Note that this risk doesn’t apply to the niacin you consume in your food.

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Written by:

Alex Evans, PharmD, MBA

Alex Evans, PharmD, MBA, has been a pharmacist for 12 years. His first job was floating in a community chain pharmacy.

Edited by:

Stacia Woodcock, PharmD

Stacia Woodcock, PharmD, is a pharmacy editor for GoodRx. She earned her Doctor of Pharmacy degree from the University of Kentucky and is licensed in New York and Massachusetts.

Reviewed by:

Patricia Weiser, PharmD

Patricia has 16 years of pharmacist experience. She previously held positions as a community pharmacist, pharmacy manager, and hospital pharmacist.

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