Back to articles
Comparative guide · 6 min read

TMG vs SAMe — methyl donor vs activated methyl carrier

Updated 2026-05-13 · Reviewed by SupplementScore editors · No sponsorships

TMG (trimethylglycine, also called betaine anhydrous) and SAMe (S-adenosylmethionine) both touch the methylation cycle, but they're not interchangeable. TMG is a methyl donor that helps regenerate methionine from homocysteine via the BHMT pathway. SAMe is the activated form of methionine that actually performs methylation reactions in the body. TMG has solid evidence for homocysteine lowering and use in CBS-deficiency or athletic performance. SAMe has trial evidence for depression, osteoarthritis, and intrahepatic cholestasis. They aren't competitors so much as different rungs of the same metabolic ladder.

Quick verdict

GoalBetter choiceWhy
Lowering elevated homocysteineTMGRCTs at 3–6 g/day show 10–20% reduction; cheap and well-tolerated.
Mild-to-moderate depressionSAMeMultiple RCTs and a meta-analysis support 800–1600 mg/day as monotherapy or SSRI adjunct.
Osteoarthritis painSAMeComparable to NSAIDs in trials at 1200 mg/day; slower onset.
Liver disease (NAFLD, alcohol-related)SAMe (with caveat)Some trial evidence for intrahepatic cholestasis; TMG also has NAFLD evidence at 20 g/day (unpalatable doses).
Athletic performance (strength / power)TMGSmall but consistent strength/power signal at 2.5 g/day; no comparable signal for SAMe.
CostTMG (much cheaper)TMG runs $5–15/month; SAMe runs $30–80/month for trial doses.

How they actually work

TMG — donates a methyl group to recycle homocysteine

Trimethylglycine has three methyl groups. Via betaine-homocysteine methyltransferase (BHMT), it donates one methyl to homocysteine, regenerating methionine and producing dimethylglycine (DMG) as the byproduct. This is parallel to the folate/B12 pathway through methionine synthase. TMG is most useful when the folate pathway is rate-limiting (low folate intake, MTHFR variants, high homocysteine despite B-vitamin replacement) or for liver/kidney tissues where BHMT activity is concentrated.

SAMe — the actual methylation currency

S-adenosylmethionine is formed when methionine is activated by ATP. It is the methyl donor for ~200 known transmethylation reactions including DNA methylation, phosphatidylcholine synthesis, creatine synthesis, catecholamine and serotonin metabolism, and cartilage proteoglycan production. After donating its methyl group, SAMe becomes SAH (S-adenosylhomocysteine) and then homocysteine — closing the cycle TMG and folate help reset.

Depression — SAMe's strongest case

SAMe has the better evidence for depression. A meta-analysis of clinical trials supports 800–1600 mg/day oral SAMe as monotherapy in mild-to-moderate depression and as an SSRI adjunct in incomplete responders. The trial-evidence base is older and not as large as for SSRIs, but the safety profile is clean. TMG has been studied as a "methylation support" adjunct in depression, but the direct effect-on-depression evidence is much weaker.

Homocysteine — TMG's strongest case

For elevated homocysteine that doesn't fully respond to folate/B12/B6 replacement, TMG 3 g twice daily reliably lowers homocysteine by 10–20% on top of B-vitamin background therapy. This is the FDA-approved use in homocystinuria (CBS deficiency). Whether homocysteine lowering reduces cardiovascular events in general populations remains debated despite the biomarker effect.

Liver and choline — under-recognised TMG role

Betaine is closely related to choline in metabolism, and dietary betaine intake correlates with NAFLD risk. RCTs in NAFLD using very high TMG doses (10–20 g/day) have shown modest hepatic improvement but doses at this level are impractical for chronic use. Reasonable use case: low-grade NAFLD with elevated homocysteine, where moderate TMG plus B-vitamin replacement addresses both.

Osteoarthritis — SAMe's other strong indication

SAMe at 1200 mg/day in trials has shown comparable pain and function improvement to NSAIDs in knee and hip osteoarthritis, with slower onset (weeks vs days) but no GI bleed risk. Reasonable alternative for users intolerant of NSAIDs.

SAMe — bipolar caution. SAMe has been reported to induce hypomania or mania in users with bipolar spectrum disorders. Avoid in bipolar I or II. Caution in users with strong family history of bipolar. Theoretical serotonin-syndrome risk on serotonergic prescriptions — coordinate with prescriber.

Dose, form, and timing

TMG: 1–3 g twice daily with meals for homocysteine lowering or general methylation support. Powder is cheap; tastes salty/savoury. Tolerated well; rare GI upset.

SAMe: 200–400 mg twice daily on empty stomach, titrated up to 800–1600 mg/day for depression or osteoarthritis. Enteric-coated tablets are essential — SAMe is unstable and most cheap unprotected products have low real-world potency. Brand and packaging integrity matter substantially.

Safety profile

TMG: well-tolerated. Mild GI effects, mild "fishy" body odour at high doses (related to TMA generation in some users with variant FMO3). May modestly raise LDL cholesterol at the very high (10–20 g) doses used in older NAFLD trials.

SAMe: well-tolerated at trial doses. GI upset, mild anxiety, or activation in some users. Bipolar precipitation risk. Caution with serotonergic medications. Pregnancy: not adequately studied — avoid unless clinically directed.

Practical rule. If your goal is methylation cycle support and you want a cheap, well-tolerated supplement that lowers homocysteine — pick TMG. If your goal is mood improvement or osteoarthritis pain relief — pick SAMe (and screen for bipolar history first). They aren't really competing in most use cases.

Combining them

The two can be stacked. Conceptually TMG feeds the methionine pool that SAMe is built from. In practice, no trial has tested combined SAMe + TMG dosing systematically for any specific endpoint; combining adds cost without clear synergistic evidence. A more sensible "methylation stack" is methylfolate + methylcobalamin + B6 (P5P), with TMG added if homocysteine remains elevated.

Who should pick each

Pick TMG if: elevated homocysteine on labs, CBS-deficiency or homocystinuria diagnosis, MTHFR variants with high homocysteine despite folate, athletic strength/power goals, low cost priority.

Pick SAMe if: mild-to-moderate depression (no bipolar history), osteoarthritis pain (NSAID-intolerant), intrahepatic cholestasis under clinical supervision.

What we'd actually buy

For methylation support with elevated homocysteine on labs: methylfolate 800 µg + methylcobalamin 1000 µg + P5P 25 mg daily, recheck homocysteine in 8 weeks; if still elevated, add TMG 3 g BID. For mild depression with no bipolar history: enteric-coated SAMe 400 mg BID for 6–8 weeks under physician awareness.

Sources

Read more: