Vitamin B12 (cobalamin)
Cyanocobalamin, Hydroxocobalamin, Methylcobalamin, Adenosylcobalamin, Vitamin B-12, Mecobalamin, Cobamamide
Forms: Cyanocobalamin and hydroxocobalamin (injections and tablets); methylcobalamin and adenosylcobalamin are supplement forms.
Water-soluble vitamin needed for red blood cells and nerves, found mainly in animal foods. Deficiency causes anaemia and nerve damage.
Legal status: Tablets are sold freely; injections are prescription medicines in many countries; varies by country. Not prohibited in sport.
What it gives
What people use it for and what the sources report. Strength is a general category from the literature: mild, clear or strong.
Purpose
Athletes and coaches believe B12, often injected, boosts red-cell production and energy: 34% of 243 elite Polish track-and-field athletes used injections, though none were deficient. It helps when there is a real deficiency, as in vegans, poor absorption or long-term metformin use.
What people seek and what studies show
In elite athletes, haemoglobin rose with B12 only from very low up to moderate levels and did not change at higher levels, so extra B12 does not add red cells when status is normal. On long-term metformin, the risk of low B12 grew with each year of use. In small trials, high-dose tablets corrected deficiency about as well as injections (low-quality evidence).
Effects
Evidence: Approved medicine — studied in people for its medical use
Sought effects by goal (as reported)
Possible side effects
Possible does not mean certain: whether they appear depends on dose, duration, individual response and monitoring. Below — what to watch for and how to notice it early.
2 possible side effects
level · how often it is reportedWhat the levels mean
Level: general category from the literature, not your personal risk
How often
- common
- reported often
- possible
- reported in some people
- rare
- reported occasionally
How to lower the risks
For 1 of 2 possible side effects there are specific ways to lower the chance: everyday measures, supplements and options a doctor may consider. For the rest — general advice. No measure removes a risk completely.
Low-level side effects
How each option helps (3)
- Adapalene — Reduces spots in many users. Redness, scaling, dryness and stinging are common early and usually ease; acne may look worse at first. Rarely, allergic swelling.
- Benzoyl peroxide — A first-line acne option. Dryness, redness and peeling are common at first; it bleaches hair and fabric; rarely, serious allergic reactions. Severe steroid acne needs a dermatologist.
- Zinc — Trials show a modest drop in inflamed spots, weaker than antibiotics; steroid acne is driven by androgens.
Check-ups and blood tests
Which tests and check-ups to do and when. This is a guide — agree the exact schedule with your doctor.
Myth & fact
“B12 shots boost energy and red blood cells.”
Only when B12 is low. In elite athletes haemoglobin did not change at higher B12 levels, yet a third of them injected it with no deficiency found.
Combinations
No specific combination notes for this substance yet. The stack check still adds up side effects that several substances share.
Sources
Possible side effects by body system, combinations, how to lower the risks and which tests to do — free.
Open the stack check