Vitamin E and L-Carnitine Do Not Cause Yellow Urine
Neither vitamin E nor L-carnitine supplements cause yellow urine as a side effect. The evidence from comprehensive guidelines and FDA drug labeling does not list urine discoloration as an adverse effect of either supplement.
Evidence from Guidelines and Drug Labels
L-Carnitine Side Effects
According to FDA drug labeling, L-carnitine supplementation at doses up to 3 g/day causes gastrointestinal side effects (nausea, vomiting, abdominal cramps, diarrhea) and a "fishy" body odor—but not yellow urine 1. The FDA label specifically documents that approximately 76% of administered L-carnitine is excreted in urine, but there is no mention of urine color changes 2.
The ESPEN 2022 micronutrient guidelines confirm these side effects at therapeutic doses, with rarer complications including muscle weakness in uremic patients and seizures in those with seizure disorders 1. Yellow urine is not documented as a side effect in any guideline or drug label.
Vitamin E Side Effects
The ESPEN 2022 guidelines detail vitamin E toxicity extensively, noting that even high doses up to 3200 IU per day cause no consistent adverse effects, with the primary concern being increased bleeding risk in those on anticoagulants 1. Urine discoloration is not mentioned as a side effect of vitamin E supplementation 1.
What Actually Causes Yellow Urine
B Vitamins Are the Culprit
Research demonstrates that B vitamins, particularly riboflavin (B2), are responsible for bright yellow urine—not vitamin E or L-carnitine 3. A controlled study showed that vitamin B2 supplementation at 200× the recommended dietary allowance dramatically increased urinary B2 concentration from 8.6 × 10⁴ to 5.7 × 10⁶ nmol/L, though interestingly, this did not always produce visible color changes in standardized assessments 3.
Other Causes to Consider
- Medications: Certain drugs like vonoprazan fumarate can cause fluorescent yellow urine under visible light 4
- Dehydration: Concentrated urine appears darker yellow
- Diet: Foods high in certain vitamins or pigments
Clinical Implications
If a patient reports yellow urine while taking vitamin E and L-carnitine:
- Review all supplements: Check for B-complex vitamins or multivitamins containing riboflavin
- Assess hydration status: Yellow urine may simply indicate concentrated urine from inadequate fluid intake
- Review medications: Certain drugs can alter urine color
- Reassure the patient: If taking B vitamins, yellow urine is a benign, expected finding
The yellow urine is almost certainly from another source—most commonly B vitamin supplementation or dehydration—not from vitamin E or L-carnitine.