This TikTok's peptide calculator advice, fact-checked

What did @wk_onthezeppy actually say?

The creator walked through how to use an online peptide calculator to figure out how many units to draw for a 0.25 mg dose of cagrilintide, reconstituted with 1 mL of bacteriostatic water in a 5 mg vial. The key takeaway they pushed: "your dose will remain the same five units" regardless of whether you use a 100-unit, 50-unit, or 30-unit insulin syringe.

This is a tutorial aimed at people new to self-reconstituting peptides at home. The math being demonstrated is real and the calculator they referenced (Prime Peptides) does exist. The instruction is practical, focused, and narrow. It does not make clinical claims about what cagrilintide does or what dose is appropriate for any individual. That restraint matters here.

Does the science back this up?

The math checks out. With 5 mg in 1 mL of solution, you have a concentration of 5 mg/mL, or 0.05 mg per 0.1 mL. On a standard U-100 insulin syringe, 5 units equals 0.05 mL, which delivers exactly 0.25 mg. That arithmetic is consistent across syringe sizes because insulin syringes use the same unit markings regardless of barrel volume.

The claim that unit markings remain consistent across 30-, 50-, and 100-unit insulin syringes is broadly correct for U-100 syringes. A unit on a U-100 syringe is always 0.01 mL. However, it is worth flagging that not all small syringes sold internationally are U-100 calibrated. U-40 syringes still exist in some markets, and drawing the same "5 units" on a U-40 syringe would deliver a different volume entirely. The creator does not mention this distinction. That is a real omission for a tutorial targeting beginners.

What did they get wrong (or right)?

They got the core math right, and using a calculator rather than doing manual arithmetic is genuinely good advice for someone new to reconstitution. Dosing errors with concentrated peptide solutions are a documented patient safety issue in compounding contexts. A 2020 review by Shrank, Rogstad, and Parekh in JAMA on medication errors noted that concentration misunderstandings are among the most common dosing mistakes in self-administered injectable therapies.

What they got wrong, or at least incomplete: the video never mentions that syringe calibration matters and that not all syringes are U-100. It also does not mention storage requirements after reconstitution, which directly affects the accuracy of subsequent doses. Reconstituted peptides stored improperly degrade, meaning later doses from the same vial may not deliver the expected amount. That is not a minor footnote for a beginner tutorial. The creator also never addresses sterile technique, which is a significant gap given the injection-site hashtag on the post.

What should you actually know?

If you are reconstituting any peptide at home, the calculator math shown in this video is a reasonable starting point. However, there are things this video leaves out that actually matter.

• Syringe calibration is not universal. Always confirm you are using a U-100 insulin syringe. U-40 syringes exist and using one with this calculation would result in a roughly 2.5x dosing error.
• Bacteriostatic water and sterile water are not interchangeable. Bacteriostatic water contains benzyl alcohol as a preservative, which extends multi-dose vial use. Sterile water has no preservative and should not be used for multi-dose vials.
• Cagrilintide is an investigational amylin analog that has only been studied in clinical trials, most notably the REDEFINE trials (Enebo et al., 2021, The Lancet) in combination with semaglutide. It is not approved by the FDA as a standalone therapeutic, and peptides sold through gray-market vendors are not subject to the manufacturing controls that apply to approved drugs.
• Peptide sourcing and quality vary enormously outside of regulated pharmacy channels. A peptide calculator can only work with what is actually in the vial, and purity is not guaranteed by the label.

This video teaches math. It does not teach safety. For a beginner audience, those two things should not be separated.