Tirzepatide: research, legal status and who sells it

What it is

Tirzepatide activates two incretin hormone receptors: those for glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) [10]. It is sold by Eli Lilly as the prescription medicines Mounjaro and Zepbound [1][2].

Research status

The evidence comes from large phase 3 trials. In SURMOUNT-1, 2,539 adults with obesity but without diabetes lost an average of 15.0% to 20.9% of body weight over 72 weeks, depending on the dose, compared with 3.1% on placebo [10]. In type 2 diabetes, SURPASS-2 found that tirzepatide lowered HbA1c more than semaglutide over 40 weeks [11]. In SURMOUNT-5, a head-to-head obesity trial, average weight loss at 72 weeks was 20.2% with tirzepatide and 13.7% with semaglutide [12]. Gastrointestinal side effects were the most common and occurred mostly while the dose was being increased [10].

Regulatory status

The FDA approved Mounjaro in May 2022 and Zepbound in November 2023 [1][2]. Mounjaro has been authorized across the EU since September 2022 [4] and is licensed in the UK [3]. Mounjaro and Zepbound are marketed in Canada [5][6], and tirzepatide is a Schedule 4 prescription-only medicine in Australia [7]. It is not named on WADA’s 2026 Prohibited List [9].

Quality and testing considerations

The FDA says unapproved GLP-1 products such as tirzepatide sold outside the approved supply chain have not been reviewed for safety, effectiveness or quality [13]. In a 2025 warning letter to a website selling “research use only” tirzepatide under Mounjaro-style names, the agency wrote that such drugs “may be contaminated, counterfeit, contain varying amounts of active ingredients, or contain different ingredients altogether” [14]. The FDA has also set up an import alert (66-80) to stop GLP-1 active ingredients with potential quality concerns from entering the US [13]. A lab report for any research-labeled vial should confirm identity by mass spectrometry and give a measured purity and content for the specific batch, because no regulator has checked its label.

Where it’s sold

Tirzepatide is legally sold only as prescription medicines such as Mounjaro and Zepbound; the tables below track unapproved “research” listings and prices.