3 rare but serious side effects of vitamin B12 supplements

Vitamin B12 (cyanocobalamin) supports the nervous system and helps your body make red blood cells. Most of the time, vitamin B12 supplements are safe and well-tolerated, but knowing the rare and serious side effects can help you recognize when something is wrong and when to seek medical attention.

1. Allergic reactions

Allergic reactions are a rare but serious side effect that can occur with any medication or vitamin. These reactions can range from mild to severe and life-threatening.

Serious reactions have been reported primarily with injectable forms of vitamin B12 rather than daily oral supplements. Seek immediate medical attention if you have symptoms of an allergic reaction, such as hives, difficulty breathing or swallowing, or swelling of the face, lips, tongue, or throat.

2. Acne and rosacea

Some research has shown that, in rare cases, vitamin B12 can trigger acne. In a small study, one in ten participants developed acne within a week of starting a vitamin B12 supplement.

Additionally, isolated cases of rosacea flare-ups associated with high-dose daily vitamin B12 supplements have been reported. However, these reports are rare. Recent studies have actually found that many people with rosacea have lower levels of vitamin B12.

However, if you are prone to skin conditions, such as acne or rosacea, consult your healthcare professional before adding a B12 supplement to your routine.

3. Hypokalemia (low potassium levels)

Hypokalemia (low potassium levels) is a rare side effect that can occur when vitamin B12 is used to treat a serious deficiency.

Vitamin B12 helps the body make new red blood cells. However, when the body begins to rapidly produce new red blood cells, potassium levels may drop. This usually only occurs in people who had very low vitamin B12 levels before starting vitamin B12 supplementation and who receive higher-dose treatment, such as injections, rather than daily supplements.

Symptoms of low potassium may include:

• Muscle weakness
• Constipation
• Fatigue
• Irregular heartbeat

If you are being treated for vitamin B12 deficiency, your doctor may monitor your potassium levels.

Who Should Not Take B12 Supplements

Vitamin B12 supplements are considered safe, even in high doses. However, it’s always a good idea to consult your doctor before adding a new vitamin or supplement to your routine.

Be sure to mention if you have ever had an allergic reaction to vitamin B12, cyanocobalamin, or cobalt, or if you have a rare inherited condition called Leber’s hereditary optic neuropathy (LHON).

What medications can cause a deficiency?

Certain medications, including prescription and over-the-counter medications, can cause low levels of vitamin B12 in your body, especially if taken for a long time.

If you take one of these medications, your doctor may monitor your levels regularly and recommend a supplement if your levels are too low:

• Metforminwhich is commonly prescribed to people with diabetes to help them manage their blood sugar levels.
• Medicines used to control acid reflux and certain gastrointestinal conditionssuch as Prilosec (omeprazole), Nexium (esomeprazole), Prevacid (lansoprazole), Pepcid (famotidine) or Tagamet (cimetidine).