TMG has quietly become a fixture in longevity and methylation stacks, usually sold as the thing you add to NMN to "keep your methylation running." It is a real, well-studied compound with one genuinely solid effect and a couple of honest caveats the marketing tends to skip. The clean summary: TMG reliably lowers homocysteine and gives a modest bump to strength, but lowering homocysteine has not translated into fewer heart attacks in trials, and at high doses TMG can nudge your cholesterol the wrong way. This guide explains what TMG is, how it works, what it realistically does, and where the hype outruns the data.
The short version
- TMG (trimethylglycine) is the same molecule as betaine, originally from sugar beets.
- Its best-established effect is lowering homocysteine, reliably and in proportion to the dose.
- But large trials that lowered homocysteine did not reduce heart attacks or strokes, so a lower number is not a proven health win.
- For exercise, the honest read is a small lower-body strength benefit at about 2.5 g a day, not a dramatic effect.
- At high doses (4 g or more) TMG can raise cholesterol, which is the main caveat.
What TMG actually is
TMG stands for trimethylglycine, and it is chemically identical to betaine, first isolated from sugar beets and also found in spinach, wheat bran, and quinoa. The name matters because it shows up in two very different places. As a supplement it is sold as TMG or "betaine anhydrous" for methylation and performance. As a medicine, that exact same betaine anhydrous is the FDA-approved drug Cystadane, used since 1996 to treat homocystinuria, a rare inherited disorder of homocysteine metabolism. So TMG is not a fringe novelty; it is a genuinely characterized molecule with a real pharmacology.
Why TMG is trending
Three separate currents pushed TMG into the spotlight. The biggest is the methylation and longevity crowd, where TMG is paired with NMN on the theory that NMN supplementation consumes methyl groups and TMG helps replenish them. The second is athletic performance, where betaine at about 2.5 grams a day is used as an ergogenic aid. The third is liver health, based on betaine's role in fat metabolism. Each of these has some scientific basis, but each also gets stretched well past what the human evidence supports, which is exactly where an honest guide earns its keep.
The mechanism
TMG's core job is simple and real: it is a methyl donor. Through an enzyme called BHMT, TMG hands a methyl group to homocysteine, converting it back into methionine and helping regenerate the body's central methylation currency (the methionine and SAMe cycle). That is a legitimate biochemical role, and it is why TMG lowers homocysteine. TMG is also an osmolyte, meaning it helps pull water into cells, which is the proposed basis for the "cellular hydration" performance angle. The methylation role is well established; the performance mechanism is more of a plausible hypothesis than a settled fact.
Homocysteine, honestly
Here is where TMG is on its firmest ground, and also where the story needs an asterisk. Human trials consistently show that TMG lowers blood homocysteine in a dose-dependent way; doses of 3 to 6 grams a day cut fasting homocysteine by roughly 10 to 15 percent, and even dietary-range doses move the needle. That part is solid.
The honest caveat is what lowering homocysteine actually buys you. High homocysteine is associated with cardiovascular risk, which led to the "homocysteine hypothesis" that lowering it should prevent heart disease. But large randomized trials that lowered homocysteine (mainly with B vitamins and folate) by around 25 percent, such as the NORVIT and HOPE-2 trials, did not reduce heart attacks or cardiovascular deaths. In other words, TMG genuinely lowers the number, but lowering that number has not been shown to prevent the events people care about. That distinction, between moving a biomarker and improving an outcome, is the single most important thing to understand about TMG.
Performance and liver
For exercise, the evidence is real but modest and a bit messy. Individual trials disagree: some found improved strength or body composition, others found little. The most recent meta-analysis, pooling 17 studies, found a significant benefit for lower-body strength at the standard 2.5 grams a day, but no clear effect on power, sprinting, or muscular endurance. So the fair summary is a small, strength-leaning benefit, not a transformative one.
On the liver, a one-year trial in people with biopsy-proven fatty liver disease used a very high 20 grams a day and improved fat accumulation but not the inflammation and scarring that actually drive the disease. That dose is roughly ten times a normal supplement dose, so it is not a template for everyday use, and the liver benefit remains preliminary.
Dosing, and TMG vs betaine HCl
Doses depend on the goal: roughly 500 to 2,000 mg a day of TMG for the methylation and homocysteine angle, and 2.5 grams a day of betaine for the performance angle. One common point of confusion is worth a table, because the two "betaines" on supplement shelves are not interchangeable:
| Supplement | What it is | Used for |
|---|---|---|
| TMG / betaine anhydrous | Trimethylglycine, a methyl donor | Methylation, homocysteine, performance |
| Betaine HCl | Betaine hydrochloride (delivers stomach acid) | Digestive support (adds gastric acid) |
If your goal is methylation, you want TMG or betaine anhydrous. Betaine HCl is a digestion product that supplies acid, not primarily methyl groups, so do not substitute one for the other.
Safety and the cholesterol caveat
At everyday doses of 0.5 to 2.5 grams a day, TMG is generally well tolerated. The points worth knowing:
- Cholesterol. This is the notable caveat. A trial at about 6 grams a day raised LDL cholesterol and triglycerides, and a meta-analysis found total cholesterol rose at doses of 4 grams a day or more. If you already have high cholesterol, keep the dose modest and be aware of this.
- GI effects. Some people get stomach upset or diarrhea, usually at higher doses.
- Fishy body odor. This can occur at very high doses (around 12 grams) and in people with a particular FMO3 enzyme variant, because betaine can be converted to trimethylamine.
- Medical supervision. If you take cardiovascular medication or are pregnant or breastfeeding, check with a clinician first.
Frequently asked questions
Is TMG the same as betaine?
Yes. Trimethylglycine (TMG) and betaine anhydrous are the same molecule, first isolated from sugar beets. The prescription drug Cystadane is pharmaceutical-grade betaine, approved for a rare genetic disorder called homocystinuria. On supplement labels, TMG and betaine anhydrous are interchangeable names for the same compound.
Does TMG lower homocysteine?
Yes, reliably and in proportion to the dose. This is its best-established effect: human trials show TMG donates a methyl group that converts homocysteine back into methionine, lowering blood homocysteine. The honest caveat is that large trials which lowered homocysteine by other means did not reduce heart attacks or strokes, so a lower number does not automatically mean fewer cardiovascular events.
Does TMG boost athletic performance?
Modestly and inconsistently. Individual trials conflict, and the most recent meta-analysis found a real but small benefit for lower-body strength at about 2.5 grams a day of betaine, with no clear effect on power, sprinting, or muscular endurance. It may help strength a little; it is not a dramatic performance enhancer.
TMG vs betaine HCl: what is the difference?
They are different supplements for different purposes. TMG (betaine anhydrous) is used as a methyl donor for methylation and homocysteine. Betaine HCl (betaine hydrochloride) is used to add stomach acid for digestion. Do not swap one for the other: betaine HCl delivers acid, not primarily methyl groups.
Does TMG raise cholesterol?
At high doses it can. A trial using about 6 grams a day raised LDL cholesterol and triglycerides, and a meta-analysis found total cholesterol rose at doses of 4 grams a day or more. Typical smaller doses of 0.5 to 2.5 grams are less studied for this, but anyone with high cholesterol should be aware of the effect and keep the dose modest.
Is TMG safe?
For most healthy adults at 0.5 to 2.5 grams a day it is well tolerated, with occasional GI upset or diarrhea. A fishy body odor can occur at very high doses and in people with a particular FMO3 enzyme variant. The main caveat is the cholesterol rise above roughly 4 grams a day. Check with a clinician if you are on cardiovascular medication or pregnant.
The bottom line
TMG is a legitimate, well-studied supplement with a clear identity: it is a methyl donor that reliably lowers homocysteine and offers a modest lower-body strength benefit. What it is not, at least on the current evidence, is a proven longevity or heart-protection agent. The leap from "lowers a biomarker" to "extends your life" is exactly the kind of marketing overreach worth resisting, and high doses carry a real cholesterol trade-off. If you are using it to support a methylation or NMN stack at a sensible dose, it is a reasonable, inexpensive choice, just with clear-eyed expectations about what it does and does not do.