Vitamin B12 shots are a common medical intervention. Many individuals receiving these injections may notice a distinct change in their urine color. This common occurrence is typically not a cause for concern, and understanding the reasons behind it can offer reassurance.
The Expected Color Change
After a vitamin B12 injection, it is common and normal for urine to appear bright yellow, neon yellow, or even reddish-orange. This color change is a harmless, temporary effect. Typically, this vivid coloration becomes noticeable within a few hours and usually subsides within a day or two, though it can persist for several days depending on the individual and dosage.
Why This Happens
Vitamin B12 (cobalamin) is a water-soluble vitamin. When administered via injection, the body rapidly absorbs the amount it needs. Any excess B12 not immediately utilized or stored is naturally processed and excreted through the kidneys into the urine.
The vibrant yellow color is primarily due to riboflavin (vitamin B2), often included in B-complex formulations or a byproduct of B12 metabolism. Riboflavin possesses a natural fluorescent yellow pigment, which imparts this striking color as it is eliminated.
Certain forms of B12, such as hydroxocobalamin, can also directly cause a reddish or dark red/purple discoloration of urine, especially when given in higher doses.
When to Seek Medical Advice
While bright yellow, neon, or reddish-orange urine after a B12 shot is expected and benign, it is important to distinguish this from true red or brown urine, medically known as hematuria. Hematuria can signal underlying health issues.
Unlike the clear, vibrant color from B12, true red or brown urine may be caused by various factors, including certain foods like beets, blackberries, or rhubarb, as well as medications such as rifampin or phenazopyridine.
More concerning causes of red or brown urine involve medical conditions, such as urinary tract infections (which might also present with pain, burning during urination, or a strong urge to urinate), kidney stones, kidney disease, an enlarged prostate in men, or certain cancers of the bladder, kidney, or prostate.
If urine appears genuinely red, cloudy, or is accompanied by symptoms such as pain, fever, chills, or persistent abdominal or back discomfort, consult a healthcare professional.