Methylated B12. The active form. Not the cheap one.

Vitamin B12 is a cofactor in two reactions that the body cannot run without it. The first is methionine synthase, which converts homocysteine to methionine and feeds the methylation cycle. The second is methylmalonyl-CoA mutase, which sits inside mitochondria and connects amino acid and fatty acid metabolism to the energy-producing machinery of the cell.¹

Translation: B12 is required for normal red blood cell formation, DNA synthesis, nervous system function, and the methylation reactions that the body uses everywhere from neurotransmitter production to gene expression regulation.²

When B12 status is low, the consequences show up across the body. Megaloblastic anemia. Fatigue. Numbness and tingling in the hands and feet. Cognitive fog. Disrupted sleep. Mood changes.³ The nervous system is especially sensitive. Neurologic symptoms can appear before anemia shows up on a blood panel, which is part of why deficiency is so frequently caught late.

For lifters, the floor matters. B12 doesn't drive performance the way caffeine does. It's infrastructure. The training adaptation, the recovery, the energy production at the cellular level: none of it runs cleanly when B12 is low.

There are two metabolically active forms of B12 in the human body: methylcobalamin and 5-deoxyadenosylcobalamin.⁴ These are the forms cells actually use. The most common form in cheap supplements is cyanocobalamin, a synthetic version that the body has to convert into the active forms before it can use it. Cyanocobalamin works. It's stable. It's inexpensive. It also has a cyanide molecule attached that the body has to remove during conversion.

Methylcobalamin is the form that participates directly in the methionine synthase reaction. No conversion step required. It's the form B12 takes when the body uses it for methylation chemistry.

The published evidence does not show methylcobalamin is dramatically better absorbed than cyanocobalamin in healthy adults.⁵ What it does show is that methylcobalamin is the active coenzyme form, the version of B12 that the cell uses without an intermediate step.⁶ For a brand built around getting the formulation right rather than getting it cheap, that's the form that goes in the pouch.

The recommended daily intake of B12 for adults is 2.4 micrograms. The dose in THRUX is 1,000 micrograms. The reason isn't that the body needs more. It's that the body absorbs less.

B12 absorption happens in two phases. The first phase is active and intrinsic-factor mediated, and it saturates around 1 to 2 micrograms per dose.⁷ Past that ceiling, additional B12 is absorbed only through passive diffusion across the gut wall, and passive absorption is inefficient, roughly 1 to 2 percent of the administered dose.⁸

That's why 1,000mcg is a standard high-potency oral B12 dose. At that level, around 10 to 20mcg of B12 actually gets absorbed depending on individual factors, still several times the daily requirement, but accounting for the inefficiency of high-dose absorption.⁹ It's the dose level used in clinical research where high-dose oral B12 has been compared to injection therapy and shown to normalize serum B12 effectively.¹⁰

For lifters whose diets aren't consistently built around B12-rich foods (anyone running long cuts, restrictive prep diets, intermittent fasting protocols, or just eating around training instead of for it), the high-potency dose is the difference between guessing and covering the floor.

B12 only naturally occurs in animal-source foods.¹¹ Meat, fish, eggs, dairy. The protein sources that anchor most lifter diets are also the primary B12 sources. So why is supplementation worth it for a serious lifter?

Because the diet isn't always consistent with the lift. Cutting phases compress total food volume. Long contest prep diets cycle the same few foods for weeks. Travel disrupts intake. Caloric restriction reduces B12 along with everything else. Older lifters absorb less B12 from food than they did in their twenties due to reduced stomach acid, which is well documented in the absorption literature.¹² Lifters using metformin or proton pump inhibitors absorb less B12 from food, also documented.¹³

None of this is exotic. It's the everyday reality of training hard while eating with intention. B12 from food is the goal. The 1,000mcg in THRUX is insurance for the days the food side doesn't carry the load.

B12 has a strong safety profile at supplemental doses. The body excretes what it doesn't use, and there is no established upper intake limit because excess B12 has not been shown to cause harm in healthy adults.¹⁴ It's a water-soluble vitamin doing infrastructure work.