How much vitamin B2 is an overdose?

January 6, 2026 •

3 min read

A toxic level of riboflavin from food or supplements has not been observed in healthy individuals. This means that experiencing an overdose of vitamin B2 is highly unlikely because your body naturally flushes out what it doesn't need.

Quick Summary

The body's limited absorption of riboflavin makes a vitamin B2 overdose virtually impossible, as excess amounts are efficiently excreted through urine.

Key Points

Overdose is Not a Concern: A toxic level of riboflavin has never been observed in humans due to its high excretion rate and limited absorption capacity.
Limited Absorption: The digestive system can only absorb about 27 mg of riboflavin from a single dose, effectively preventing an overdose from supplements.
Excess is Excreted: As a water-soluble vitamin, any excess B2 is filtered by the kidneys and harmlessly expelled in the urine, causing a bright yellow discoloration.
No Tolerable Upper Intake Level: No upper limit has been established for riboflavin, as there is no evidence of toxicity from high intakes.
Minor Side Effects: Very high supplemental doses may cause temporary side effects such as nausea, diarrhea, or harmless bright yellow urine.
Consult a Professional: While safe for most, high-dose supplementation should be discussed with a doctor, especially for individuals with other health conditions or taking medication.

What is a Vitamin B2 Overdose?

An overdose, or toxicity, refers to a harmful accumulation of a substance in the body. In the case of vitamin B2, also known as riboflavin, an overdose is not a concern for healthy individuals. As a water-soluble vitamin, riboflavin does not accumulate in the body's tissues in the same way that fat-soluble vitamins (A, D, E, K) can. Instead, the body only absorbs what it needs and any surplus is filtered by the kidneys and expelled in the urine, a process known as flavinuria. This natural excretion mechanism is the primary reason why a toxic level from oral intake has never been established.

The Water-Soluble Advantage

The body's limited absorption capacity for riboflavin is a key protective factor against overdose. When you consume a single, large dose of riboflavin, the small intestine becomes saturated and can only absorb a maximum of about 27 mg at a time. Any amount beyond this limit is not absorbed and passes through the digestive tract. This built-in safety feature prevents toxic levels from building up, even with high-dose supplementation.

Potential Side Effects of High Doses

While a true overdose is not possible, very high doses of riboflavin, particularly from supplements, can cause some minor and harmless side effects. These are typically temporary and resolve once intake is reduced.

Key side effects associated with high vitamin B2 intake include:

Bright Yellow Urine: This is the most common and harmless side effect, a direct result of excess riboflavin being excreted.
Nausea: Some individuals have reported mild stomach upset when taking very high doses.
Diarrhea: In some cases, high intake may lead to diarrhea.
Increased Urination: Due to its water-soluble nature, a higher intake can lead to increased urine output.

Clinical studies, such as those involving the use of high-dose riboflavin for migraine prophylaxis, have confirmed the safety profile. For instance, a trial administering 400 mg of riboflavin daily for several months found no significant adverse effects.

Recommended Daily Allowance vs. High Intake

It is important to distinguish between the recommended dietary allowance (RDA) and the significantly higher doses sometimes used in clinical settings or found in supplements. The RDA represents the average daily intake sufficient to meet the nutrient requirements of nearly all healthy individuals.

Vitamin B2 Dosage Comparison


Metric	RDA for Adult Male (19-70 yrs)	RDA for Adult Female (19-70 yrs)	High Dose (Clinical Study)	Comments
Daily Intake	1.3 mg	1.1 mg	Up to 400 mg daily	High doses are typically for specific medical purposes under supervision.
Absorption Limit	Well within absorption capacity	Well within absorption capacity	Exceeds absorption capacity (~27 mg)	Excess amounts are excreted, preventing toxicity.
Known Toxicity	None	None	None reported from oral intake	No Tolerable Upper Intake Level (UL) has been set.

Comparative Risk: B2 vs. Other B Vitamins

While vitamin B2 poses a minimal risk of overdose, the same cannot be said for all B vitamins. The risk of toxicity varies within the B-complex family. For example, excessive, long-term intake of vitamin B6 (pyridoxine) from supplements can cause nerve damage, and very high doses of vitamin B3 (niacin) can lead to skin flushing and liver toxicity. This is why relying on a balanced diet for vitamins is always preferable unless a supplement is recommended by a healthcare provider.

Conclusion

In conclusion, a true overdose of vitamin B2 is extremely unlikely due to its water-soluble properties and the body's limited capacity for absorption. While very high supplemental doses may cause temporary, minor side effects like bright yellow urine, nausea, or diarrhea, these are not considered toxic or life-threatening. Health organizations have not established a Tolerable Upper Intake Level for riboflavin, reflecting its high safety profile. Always consult a healthcare professional before taking high-dose supplements, particularly if you have underlying health conditions or are on other medications.

For more information on the use of high-dose riboflavin in a clinical setting, you can read about its application for migraine prevention.

Frequently Asked Questions

No, it is highly unlikely to overdose on vitamin B2. As a water-soluble vitamin, your body simply excretes any excess riboflavin it does not need through urine, preventing a toxic buildup.

If you take very high doses of vitamin B2, the most common side effect is harmless, bright yellow urine. In some instances, mild and temporary side effects like nausea or diarrhea may occur.

A vitamin B2 overdose isn't a risk because your body has a natural safety mechanism. The small intestine can only absorb a limited amount of riboflavin at one time (about 27 mg), and any amount over that is excreted.

No, bright yellow urine after taking riboflavin is a harmless and expected side effect, not a sign of an overdose. It is simply the body eliminating the excess vitamin it did not absorb.

Major health organizations have not established a Tolerable Upper Intake Level (UL) for riboflavin, as no toxic effects have been observed from high doses from food or supplements.

High doses of vitamin B2 could potentially interfere with certain medications, including some antipsychotics, antibiotics, and drugs for gout or cancer. You should always consult a healthcare provider if you are taking medication before starting a high-dose supplement.

In some clinical settings for migraine prevention, doses of up to 400 mg daily have been used under medical supervision. However, this is significantly higher than the typical recommended daily allowance and is not necessary for general health.

B2 supplements are generally considered safe, especially at or near recommended dosages. The risk of toxicity is extremely low. However, you should still consult a doctor before starting any new supplement.