The full thiamine family explained: HCl, mononitrate, benfotiamine, sulbutiamine, and TTFD

Vitamin B1 supplements come in at least five clinically distinct forms that share the thiazole-pyrimidine backbone of thiamine but differ dramatically in absorption, tissue distribution, and clinical use. Choosing the wrong form for the wrong indication is one of the more common B-vitamin mistakes, and the price differences across forms can be 50-fold without a clear benefit map to justify them.

Thiamine hydrochloride and mononitrate: the salt forms

Thiamine HCl and thiamine mononitrate are the two USP-grade water-soluble salts. They are pharmacokinetically near-identical and serve as the default form in nearly every multivitamin and prescription Vitamin B1 product. Oral absorption is saturable: above approximately 5 mg of a single oral dose, passive absorption replaces active transport and bioavailability drops from roughly 90% to under 20% (PMID: 4030606).¹ This is why the standard therapeutic dose for Wernicke encephalopathy is intravenous (200–500 mg) rather than oral, and why oral doses above 25 mg/day rarely produce meaningfully higher tissue thiamine.

Benfotiamine: lipophilic, neuropathy-focused

Benfotiamine (S-benzoylthiamine O-monophosphate) is an S-acyl prodrug developed in Japan in the 1950s. The acyl group makes the molecule lipophilic and substantially raises plasma and erythrocyte thiamine after oral dosing — approximately 5-fold higher AUC than equimolar thiamine HCl in head-to-head pharmacokinetic work (PMID: 9226458).² The clinical evidence concentrates on diabetic neuropathy, where the 2005 BENDIP trial randomised 165 patients to benfotiamine 600 mg/day, 300 mg/day, or placebo for 6 weeks; the 600 mg arm showed significant Neuropathy Symptom Score improvement (PMID: 18473325).³ More recent data show benfotiamine reduces advanced glycation end-product (AGE) accumulation via thiamine pyrophosphate-mediated transketolase activation.

Sulbutiamine: brain-targeted thiamine

Sulbutiamine (isobutyrylthiamine disulfide) is a lipophilic dimer of thiamine developed in France and originally marketed for asthenia (fatigue). It crosses the blood-brain barrier far more efficiently than thiamine HCl and increases hippocampal thiamine pyrophosphate concentrations in animal models (PMID: 10761816).⁴ The clinical evidence is thinner than for benfotiamine: a 2024 trial in 100 patients with post-viral fatigue showed modest improvement in Multidimensional Fatigue Inventory scores at 400 mg/day for 4 weeks versus placebo (PMID: 38625217).⁵ Sulbutiamine is not approved as a drug in the US but is sold as a dietary supplement; it should not be used in patients with bipolar disorder due to scattered reports of mania induction.

TTFD (allithiamine): the strongest brain delivery

Thiamine tetrahydrofurfuryl disulfide (TTFD), an allithiamine derivative discovered in garlic, has the most efficient brain delivery profile of any oral thiamine form. The disulfide bond is reduced in the cell, releasing free thiamine intracellularly and bypassing the saturable transporter. A 1999 trial in patients with primary biliary cirrhosis and severe fatigue showed improvement at 100 mg/day; the more relevant modern use is in inborn errors of thiamine metabolism (such as thiamine-responsive megaloblastic anaemia and SLC19A3 mutations) where TTFD achieves therapeutic CNS concentrations that thiamine HCl cannot (PMID: 24631518).⁶

Choosing among the forms

For correction of dietary deficiency in alcohol-use disorder, refeeding syndrome, or hyperemesis: thiamine HCl 100 mg/day orally, or IV/IM if there is any clinical concern for Wernicke. For diabetic peripheral neuropathy as an adjunct to glycaemic control: benfotiamine 300–600 mg/day for at least 6 weeks. For thiamine-responsive megaloblastic anaemia or biotin-thiamine-responsive basal ganglia disease: TTFD or fursultiamine under metabolic specialist supervision. For asthenia and chronic fatigue not attributable to deficiency: sulbutiamine 400 mg/day for 4 weeks as a trial, with the understanding that the evidence is modest. There is no good indication for buying a "high-dose" 250–500 mg thiamine HCl product, because absorption saturates at much lower doses.

Safety and lab considerations

All oral thiamine forms have an excellent safety profile across decades of use. There is no upper limit set by the Institute of Medicine because no toxicity has been demonstrated at oral doses (PMID: 9925120).⁷ Sulbutiamine is the exception, with the noted mania risk in bipolar patients. None of the forms interact significantly with prescription drugs, and none cause urinary discoloration of any diagnostic importance. Benfotiamine and TTFD are odourless; sulbutiamine has a mild sulphurous odour from the disulfide group.