Semaglutide research vials swing more than 2× in $/mg across vendors for the same 4,113 Da molecule. Cheapest per mg today among the vendors we list: $2.93/mg, on Ion Peptide's 20mg vial at $58.65 (15% off with code thepeptidecatalog). Bigger vials cost less per mg, but a reconstituted vial is typically kept no longer than 28 days, so the lowest $/mg is not always the lowest cost for a small weekly amount. The real question isn't "what's cheapest," though — it's "which vendor's COA actually matches the vial." Semaglutide is a 31-amino-acid GLP-1 analog with a C18 fatty-diacid side chain; synthesis is expensive and counterfeits are common.
This guide covers what you should actually pay per milligram, which vial size fits a community titration protocol, how to verify a COA for a modified peptide, and the vendor red flags to avoid.
Research-context information only. Semaglutide is the active ingredient in FDA-approved products for type 2 diabetes and chronic weight management; research-peptide and compounded forms are not FDA-approved and are sold for research purposes only. Protocols, doses, and reactions reported below come from clinical trials and community sources. This article reports what has been documented, not what should be done. Consult a licensed physician for personal medical decisions.
This is not a ranked vendor list — for that, see our Best Semaglutide Vendors comparison. This guide teaches you how to evaluate any vendor yourself.
Understanding Semaglutide Pricing
Semaglutide is sold as a lyophilized powder in sealed glass vials. The three factors that move price: vial size, manufacturer sourcing (US-synthesized costs more than overseas), and whether the vendor invests in third-party testing.
Current Market Pricing (2026)
| Vial size | Lowest price today (with code) | Vendor | Also sold by (price today) |
|---|---|---|---|
| 5mg | $19.00 ($3.80/mg) | Ascension Peptides | Ion Peptide $33.15 · EZ Peptides $24.30 |
| 10mg | $30.60 ($3.06/mg) | EZ Peptides | Nura Peptide $38.50 · Mile High Compounds $53.99 |
| 20mg | $58.65 ($2.93/mg) | Ion Peptide | — |
Prices are single vials through our links, with each vendor's standing code or link discount applied.
The pattern: 5mg vials are described for titration and low-dose protocols, 10mg is the most popular size, and 15mg and 20mg vials suit extended protocols. Larger vials generally cost less per mg than the 5mg vial, though the cheapest $/mg size varies by vendor (prices by size above). But since semaglutide is dosed once weekly with a 28-day stability window, you need reconstitution discipline at the larger sizes.
Single-vial option: 15% off with code thepeptidecatalog puts Ion Peptide's 20mg semaglutide vial at $58.65 ($2.93/mg) today. Get the code →
Cost Per Week at Common Doses
Today's single-vial prices for the two sizes in this table: Nura Peptide's 10mg vial at $38.50 and Ion Peptide's 20mg vial at $58.65, each with the vendor's code. Monthly cost is the mg per month times the vial's $/mg.
| Weekly Dose | mg per Month (~4.3 weeks) | 10mg Vial Covers | 20mg Vial Covers |
|---|---|---|---|
| 250 mcg/week (community protocol; also the FDA-label starting step) | ~1.1 mg | 40 weeks | 80 weeks |
| 1 mg/week (FDA-label titration step) | ~4.3 mg | 10 weeks | 20 weeks |
| 2.4 mg/week (STEP 1 dose) | ~10.3 mg | ~4.2 weeks | ~8.3 weeks |
For current vendor-specific pricing with exact $/mg breakdowns, see our Best Semaglutide Vendors comparison.
How to Verify Semaglutide Quality
Semaglutide is a 31-amino-acid peptide with three key modifications: an alanine-to-Aib substitution at position 8, a lysine-to-arginine substitution at position 34, and a C18 fatty-diacid side chain attached to lysine-26 via a γ-Glu-ADO-ADO linker. These modifications are what extend its half-life to ~7 days — and they're expensive to synthesize correctly. A cheap manufacturer skipping the fatty-acid conjugation produces a peptide that technically has the right backbone but doesn't work.
What a COA (Certificate of Analysis) Should Include
Identity Confirmation
- Mass spectrometry confirming the correct molecular weight (4,113.58 Da for semaglutide)
- Amino acid sequence verification with Aib-8 and Arg-34 modifications
- Confirmation of the C18 fatty-diacid side chain conjugation on lysine-26
Purity Testing
- HPLC purity — look for 98%+ purity
- The chromatogram should show a single dominant peak with minimal des-acyl or truncated impurities
Contamination Testing
- Endotoxin levels (bacterial contamination)
- Residual solvent analysis (acetonitrile, TFA)
- Heavy metals screening
How to Verify a COA Is Legitimate
-
Check the testing lab — Reputable labs include Janoshik Analytical, MZ Biolabs, and Colmaric Analyticals. Avoid vendors who only show "in-house" testing.
-
Verify on the lab's website — Janoshik COAs have a task number you can look up directly at janoshik.com. If the vendor won't provide a verifiable task number, that's a red flag.
-
Check the date — COAs should be recent (within 6 months). Old COAs may not represent the current batch.
-
Match the batch — The batch/lot number on the COA should match what's printed on your vial.
-
Look for the original PDF — Screenshots are easier to fake than full PDFs with lab letterhead and signatures.
Red Flags to Avoid
- No COA available — any vendor unwilling to provide testing results is not worth the risk for a peptide this complex
- Only in-house testing — self-reported purity numbers are meaningless
- Prices well below $3/mg across all sizes — synthesis costs make this implausible without corner-cutting on the fatty-acid conjugation
- No contact information — legitimate vendors have real customer service
- Cryptocurrency only — good vendors accept crypto but also standard payment rails
- No return or reship policy — reputable vendors stand behind their products
