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Thiamine (Vitamin B1)
Bottom line
In our scoring, Thiamine (Vitamin B1) rates likely effective: the research is fairly solid for deficiency states. Our top-scored product is NOW Foods Vitamin B-1 (Thiamine HCl) 100 mg (84/100), about $0.06 a day at a clinical dose of RDA ~1.1-1.2 mg/day. Bottom line: a reasonable pick if it fits your goal. This is our opinion, not medical advice; talk to your clinician before starting.
Here is the fact that reframes this whole shelf: your gut can only pull in so much thiamine at once.
- Evidence
- Likely Effective
- Category
- Vitamins & Minerals
- Best form
- thiamine HCl or mononitrate - therapeutically equivalent, pick on price
- Effective dose
- RDA ~1.1-1.2 mg/day
- Lab tested
- 3 of 6 products
- Category
- Vitamins & Minerals
- Best form
- thiamine HCl or mononitrate - therapeutically equivalent, pick on price
- Effective dose
- RDA ~1.1-1.2 mg/day
- Lab tested
- 3 of 6 products
Key takeaways
- →Oral thiamine absorption is capped near 5 mg per dose - a 100 or 500 mg tablet does not deliver anything like its label into your blood; most is excreted (NIH ODS).
- →The honest use is repletion, not a metabolic megadose. Deficiency correction (most often from chronic heavy alcohol use in wealthy countries) is unambiguous standard of care.
- →Thiamine HCl and thiamine mononitrate are therapeutically equivalent - buy on price. If you want to beat the absorption cap, that is what benfotiamine (a separate, fat-soluble product) is for.
- →One of the safest vitamins: the FNB set no upper limit because excess is simply excreted. The one serious reaction (anaphylactoid) is tied to rapid IV use in clinics, not oral tablets.
What Is Thiamine (Vitamin B1)?
Here is the fact that reframes this whole shelf: your gut can only pull in so much thiamine at once. Oral absorption saturates near 5 mg per dose. Above that, the active transporters (SLC19A2 and SLC19A3) are maxed out and the extra rides through and out in urine; at gram doses the NIH Office of Dietary Supplements estimates only about 5% is actually taken up. So a 100 mg or 500 mg tablet does not put 100 or 500 mg into your bloodstream - most of the pill is excreted. That single ceiling is why the fat-soluble derivative benfotiamine exists as a separate product (we score it on its own scorecard): it bypasses the cap.
That does not make high-dose oral thiamine useless. It makes it a coverage tool rather than a metabolic megadose. If you are genuinely short on B1 - which in wealthy countries most often traces to chronic heavy alcohol use, not diet - repletion is not optional, it is standard care, and the surplus a big tablet delivers is a cheap way to be sure you have crossed the line into "enough." Wernicke encephalopathy, the acute deficiency emergency, is treated with parenteral (injected) thiamine precisely because you cannot flood the tissue fast enough by mouth.
Where the evidence thins out is the pitch that a replete, well-fed person should take 100 to 500 mg for energy or metabolism. There is little to support a benefit beyond simply meeting the roughly 1.1 to 1.2 mg RDA, and the absorption cap means most of that tablet never gets in anyway. One small pilot regressed an early kidney marker in type 2 diabetes at high oral doses, but it is a single 40-person study on a surrogate endpoint, unreplicated, and works against the same ceiling. Promising to watch, not a reason to dose.
Practical read: if you eat normally, you almost certainly already get your ~1.1 mg from pork, whole grains, legumes, and fortified foods without trying. Thiamine HCl and thiamine mononitrate are therapeutically equivalent, so buy on price. And it is one of the safest vitamins there is - the ceiling that limits its usefulness is the same reason it is nearly impossible to overdo by mouth.
Does It Work? The Evidence
How A-F grades workThiamine (Vitamin B1) earns a Likely Effective rating on the strength of its best-supported use: corrects deficiency states (beriberi, Wernicke encephalopathy) (grade A). The table below grades every claimed benefit on its own, including weaker and more heavily marketed uses, so one strong result never stands in for the rest.
Corrects deficiency states (beriberi, Wernicke encephalopathy)
Galvin et al. 2010 (EFNS guidelines, Eur J Neurol): Wernicke encephalopathy is a thiamine-deficiency emergency treated with parenteral thiamine; deficiency correction is unambiguous standard of care. NIH ODS: chronic alcohol use is the most common cause of deficiency in industrialized nations.
Repletion in alcohol-use disorder (Wernicke-Korsakoff prevention)
Day et al. 2013 (Cochrane review): only one small RCT met inclusion; evidence is insufficient to guide exact dose or route, so repletion rests on clinical consensus - standard of care, but the trial evidence base is thin (the hedge is the finding).
High-dose thiamine for early diabetic kidney markers
Rabbani et al. 2009 (Diabetologia) pilot (40 patients): 3x100 mg/day for 3 months regressed urinary albumin vs placebo - a single small pilot, surrogate endpoint, unreplicated, and undercut by the oral absorption ceiling.
High-dose oral thiamine as a metabolic 'megadose' for replete people
There is little benefit beyond meeting the ~1.1-1.2 mg RDA for a non-deficient person, and the oral absorption cap (NIH ODS: absorption declines above ~5 mg) means most of a 100-500 mg tablet is excreted rather than used.
| Grade | Claimed Benefit | Key Studies | Our Verdict |
|---|---|---|---|
| A | Corrects deficiency states (beriberi, Wernicke encephalopathy) | Galvin et al. 2010 (EFNS guidelines, Eur J Neurol): Wernicke encephalopathy is a thiamine-deficiency emergency treated with parenteral thiamine; deficiency correction is unambiguous standard of care. NIH ODS: chronic alcohol use is the most common cause of deficiency in industrialized nations. | Supported |
| B | Repletion in alcohol-use disorder (Wernicke-Korsakoff prevention) | Day et al. 2013 (Cochrane review): only one small RCT met inclusion; evidence is insufficient to guide exact dose or route, so repletion rests on clinical consensus - standard of care, but the trial evidence base is thin (the hedge is the finding). | Supported |
| D | High-dose thiamine for early diabetic kidney markers | Rabbani et al. 2009 (Diabetologia) pilot (40 patients): 3x100 mg/day for 3 months regressed urinary albumin vs placebo - a single small pilot, surrogate endpoint, unreplicated, and undercut by the oral absorption ceiling. | Early Signal |
| D | High-dose oral thiamine as a metabolic 'megadose' for replete people | There is little benefit beyond meeting the ~1.1-1.2 mg RDA for a non-deficient person, and the oral absorption cap (NIH ODS: absorption declines above ~5 mg) means most of a 100-500 mg tablet is excreted rather than used. | Not There Yet |
How to Choose: Forms, Doses & What Matters
Clinical dose: RDA ~1.1-1.2 mg/day; OTC repletion products sell 100-500 mg; oral absorption is capped near 5 mg per dose
Best forms: thiamine HCl or mononitrate - therapeutically equivalent, pick on price, benfotiamine is the fat-soluble derivative that beats the oral absorption cap (a separate profile), most people meet the ~1.1 mg need from diet easily
For general coverage, any dose at or a little above the ~1.1 to 1.2 mg RDA is plenty, and most people do not need a supplement at all. High-dose repletion products (100 to 500 mg) are used for documented or suspected deficiency - take one daily, with or without food, since thiamine is water-soluble and well tolerated. Keep in mind the practical ceiling: because oral absorption saturates near 5 mg per dose, splitting a very large dose across the day nudges total uptake up a little, but you cannot force a 500 mg tablet to behave like 500 mg absorbed. If you specifically want higher tissue levels, benfotiamine is the fat-soluble form designed to get past that cap. Powders are self-measured, so hitting a precise 100 mg without a milligram scale is guesswork - capsules are the easier way to dose accurately.
Who Should Take Thiamine (Vitamin B1)?
The clear case is genuine repletion. If you drink heavily (chronic alcohol use is the most common cause of B1 deficiency in wealthy countries), have a malabsorptive condition, or are recovering from a period of very poor intake, a high-dose oral tablet is a cheap, safe way to be sure you have crossed into adequacy - the surplus above the ~5 mg absorption cap is the point, since it guarantees you clear the line. It is also reasonable low-cost insurance if you are eating substantially less than usual and want to shore up a water-soluble vitamin that falls when intake drops. For beating the absorption ceiling on purpose, the fat-soluble derivative benfotiamine is the tool built for that job.
Who Should Avoid It?
Not for everyone
Side Effects & Safety
Product Scores
6 products scored on dosing accuracy, third-party testing, cost per effective dose, and label transparency.
The Scorecard: 6 Products Compared
NOW Foods Vitamin B-1 (Thiamine HCl) 100 mg
NOW Foods$6.00 ÷ 100 days at 100mg/day (1 serving × 100mg)
Our Top Pick: a recognized brand with audited in-house manufacturing at the right sensible dose, and after a price drop it is now the cheapest per dose here too (~$0.06/day). Form (HCl) is equivalent to mononitrate, so this comes down to brand track record and cost.
Prices checked 2026-07-07. Cost shown is per clinically effective daily dose, not per pill.
Nutricost Vitamin B1 (Thiamine Mononitrate) 100 mg
Nutricost$9.99 ÷ 125 days at 100mg/day (1 serving × 100mg)
The value pick: a clean 100 mg B1 at ~$0.08/day, and the only option here with a real third-party testing claim behind it. Mononitrate vs HCl makes no efficacy difference.
Prices checked 2026-07-07. Cost shown is per clinically effective daily dose, not per pill.
Solgar Vitamin B1 (Thiamin HCl) 100 mg
Solgar$17.99 ÷ 100 days at 100mg/day (1 serving × 100mg)
A legacy-brand 100 mg B1 in the equivalent HCl form. Fine quality, but at ~$0.18/day it is now the most expensive per dose here, and in our view you are paying a steep brand premium for the same active ingredient the budget options provide.
Prices checked 2026-07-07. Cost shown is per clinically effective daily dose, not per pill.
Nutricost Vitamin B1 (Thiamine Mononitrate) 500 mg
Nutricost$14.98 ÷ 115 days at 500mg/day (1 serving × 500mg)
A popular high-dose SKU, but the 500 mg label oversells what your gut can take in - oral absorption caps out near 5 mg, so most of this tablet is excreted. Fine for guaranteeing repletion; not a reason to pay for the bigger number.
Prices checked 2026-07-07. Cost shown is per clinically effective daily dose, not per pill.
Solgar Vitamin B1 (Thiamin HCl) 500 mg Super Potency
Solgar$16.06 ÷ 100 days at 500mg/day (1 serving × 500mg)
The 'Super Potency' framing sells a dose your gut cannot fully take in - absorption caps near 5 mg. A legacy brand at a premium price for a high number that mostly ends up excreted.
Prices checked 2026-07-07. Cost shown is per clinically effective daily dose, not per pill.
BulkSupplements Thiamine HCl Powder
BulkSupplements
$16.96 ÷ 1696 days at ~147mg/day (1.5 servings × 100mg)
The lowest per-gram price here, but it is dose-your-own: without a milligram scale, hitting a precise 100 mg is guesswork, so it is not the clean value pick the sticker price implies.
Prices checked 2026-07-07. Cost shown is per clinically effective daily dose, not per pill.
Full Comparison
| Category | NOW Foods Vitamin B-1 (Thiamine HCl) 100 mg NOW Foods | Nutricost Vitamin B1 (Thiamine Mononitrate) 100 mg Nutricost | Solgar Vitamin B1 (Thiamin HCl) 100 mg Solgar | Nutricost Vitamin B1 (Thiamine Mononitrate) 500 mg Nutricost | Solgar Vitamin B1 (Thiamin HCl) 500 mg Super Potency Solgar | BulkSupplements Thiamine HCl Powder BulkSupplements |
|---|---|---|---|---|---|---|
| Brand Score | 84/100Winner | 82/100 | 78/100 | 76/100 | 73/100 | 72/100 |
| Dosing & Form | 24/25Winner | 24/25 | 24/25 | 20/25 | 20/25 | 17/25 |
| Purity | 19/25Winner | 18/25 | 18/25 | 18/25 | 18/25 | 18/25 |
| Value | 22/25Winner | 22/25 | 16/25 | 20/25 | 15/25 | 20/25 |
| Transparency | 19/25 | 18/25 | 20/25Winner | 18/25 | 20/25 | 17/25 |
| Cost/Day | $0.06 | $0.08 | $0.18 | $0.13 | $0.16 | $0.01Winner |
| Dose/Serving | 100mg | 100mg | 100mg | 500mg | 500mg | 100mg |
| Form | thiamine HCl tablet | thiamine mononitrate capsule | thiamin HCl veg capsule | thiamine mononitrate capsule | thiamin HCl tablet | thiamine HCl powder (self-measured) |
| Third-Party Tested | No | ✓ Yes | No | ✓ Yes | No | ✓ Yes |
| Proprietary Blend | No | No | No | No | No | No |
Frequently Asked Questions
Does a 500 mg thiamine tablet actually give me 500 mg?
No - and this is the single most important thing to understand about oral thiamine. Absorption is capped: it declines sharply above about 5 mg per dose because the active transporters that carry thiamine across the gut wall (SLC19A2 and SLC19A3) saturate around 2.5 to 5 mg. At gram doses, the NIH Office of Dietary Supplements estimates only about 5% is actually taken up. So most of a 100 or 500 mg tablet passes through and is excreted in urine. A big oral dose is useful for guaranteeing you cross into adequacy during repletion, not for flooding your tissues.
Do I need a thiamine supplement if I eat a normal diet?
Almost certainly not. The RDA is only about 1.1 to 1.2 mg per day, and that is easy to meet from pork, whole grains, legumes, nuts, seeds, and fortified foods like breakfast cereals and bread. Deficiency in wealthy countries is uncommon and most often traces to chronic heavy alcohol use, malabsorption, or a stretch of very poor intake - not an ordinary mixed diet. If none of those apply to you, a high-dose B1 tablet is spending money on a dose your body cannot absorb.
What is the difference between thiamine HCl and thiamine mononitrate?
For your purposes, essentially nothing. Both are standard water-soluble salt forms of vitamin B1 and are therapeutically equivalent - neither is meaningfully better absorbed or more effective than the other. Mononitrate is a bit more shelf-stable, which is why it shows up more often in fortified foods, but as a supplement the two are interchangeable. Buy whichever is cheaper at the dose you want.
How is benfotiamine different from regular thiamine?
Benfotiamine is a fat-soluble derivative of thiamine, and its whole reason for existing is that it gets past the oral absorption ceiling that limits regular water-soluble thiamine. Because it dissolves in fat, it raises blood and tissue thiamine levels substantially more than the same dose of thiamine HCl or mononitrate. If your goal is simply to correct or cover a deficiency, plain thiamine is fine and cheaper. If you specifically want higher tissue levels - the target of most metabolic and nerve-comfort marketing - benfotiamine is the form built for that, and we cover it in a separate profile.
Is high-dose thiamine safe?
By mouth, yes - it is one of the safest vitamins there is. The Food and Nutrition Board set no upper intake limit because no adverse effects have been documented from high oral intake; whatever your gut cannot absorb is excreted. The one serious reaction people sometimes hear about, a severe anaphylactoid response, is tied to rapid intravenous administration in hospital settings, not to swallowing an OTC tablet. Mild stomach upset is the most a supplement is likely to cause.
Can thiamine help with diabetes or kidney problems?
The evidence is thin and early. A small 40-person pilot found that high-dose oral thiamine (3 x 100 mg/day) regressed an early urinary kidney marker in type 2 diabetes over three months. That is a single unreplicated study on a surrogate endpoint, and it runs into the same absorption cap that limits every high oral dose. It is a signal worth watching, not a reason to start dosing - discuss any diabetes or kidney concern with your doctor rather than self-treating with a supplement.
Sources
- Galvin R, et al. EFNS guidelines for diagnosis, therapy and prevention of Wernicke encephalopathy. Eur J Neurol. 2010;17(12):1408-1418.
- Day E, et al. Thiamine for prevention and treatment of Wernicke-Korsakoff Syndrome in people who abuse alcohol. Cochrane Database Syst Rev. 2013;(7):CD004033.
- Rabbani N, et al. High-dose thiamine therapy for patients with type 2 diabetes and microalbuminuria: a randomised, double-blind placebo-controlled pilot study. Diabetologia. 2009;52(2):208-212.
- NIH Office of Dietary Supplements. Thiamin Fact Sheet for Health Professionals.
Scores and tiers are our independent opinion, formed by applying a published rubric to label data, third-party certifications, and the research record. They are not statements of objective fact about a product and not a lab test. Where we report a brand-specific fact, it comes from a cited source or a public certification; where verification is missing, we say so rather than assume a result.
FDA Disclaimer: These statements have not been evaluated by the Food and Drug Administration. Dietary supplements are not intended to diagnose, treat, cure, or prevent any disease. Always consult with a qualified healthcare professional before starting any supplement regimen.