Retatrutide and thiamine B1: what is currently known

Retatrutide is an investigational once-weekly triple receptor agonist — GIP, GLP-1 and glucagon — under development for obesity and type 2 diabetes. In the published phase 2 obesity trial it produced dose-dependent weight loss of up to −24.2% at 48 weeks, with a predominantly gastrointestinal, dose-related adverse-event profile; the first phase 3 trial (TRANSCEND-T2D-1, 537 participants) reported −11.5% to −15.3% bodyweight at 40 weeks, with gastrointestinal events the most frequent adverse events.

Thiamine — vitamin B1 — is an essential micronutrient converted in the body to thiamine diphosphate, a coenzyme required for cellular energy metabolism, carbohydrate and amino-acid metabolism and normal nervous-system function. Humans maintain limited thiamine reserves.

What connects them is not a drug–vitamin interaction. No published study establishes that retatrutide chemically depletes thiamine. The connection is physiological context: retatrutide suppresses appetite strongly and frequently causes nausea and vomiting, and thiamine deficiency is the classic consequence of sustained low intake with persistent vomiting during rapid weight loss. Panacea Bio Chem describes this as retatrutide-associated nutritional vulnerability.

Reta-B1™ is the formulation response under investigation: a 5 mg retatrutide lower layer and a 20 mg thiamine upper layer, co-lyophilised as a dual-layer Peptourbillon™ inside Lyoprester SS™ and reconstituted with 0.5 mL P-EARLs™ immediately before use.