How do the major peptides rank by the strength of their published evidence?

The short answer

Peptides span a huge range of evidence quality, and lumping them together as "peptides" hides that. So we graded the ones we cover on a single scannable scale — S to F — by the strength of their published human evidence.

Evidence tier: This report card is built on our Tier 1–5 evidence framework. The letter grade is a consumer-facing summary of where a peptide sits: S maps to Tier 1, A to Tier 2, B to Tier 3, C to Tier 4, D to Tier 5. Safety and approval status factor into the grade alongside raw evidence.

The headline of the whole exercise:

• Only the GLP-1 drugs earn an S — semaglutide and tirzepatide, on large human trials and approval.
• A handful reach A — real trials or approvals for a specific use.
• Most sit B–C — promising-but-thin, or mechanism plus geographically-limited human data.
• Several popular compounds land at D — striking mechanisms, little human outcome evidence.

Crucially, a grade rates the evidence, not whether you should take something. It's a map of where the science is strong versus speculative. The full breakdown follows.

How do the grades work?

Evidence tier: 2 — the grading rubric is a transparent mapping of established evidence categories.

Each peptide is graded by the strength of published human evidence for its best-supported use, with safety and approval status taken into account:

• S — approved-drug-level human evidence. Multiple large human RCTs and/or regulatory approval; the standard regulated medicines meet.
• A — robust trials or approval for a specific indication. Strong human data or an approval, often narrower in scope.
• B — promising human plus replicated animal data. Real signal, not yet confirmed by large human trials.
• C — mechanism plus thin or geographically-limited human data. A coherent rationale and some human use, but the evidence is sparse or hard to evaluate.
• D — mechanism and marketing. Plausible biology and often animal data, but little or no human outcome evidence.
• F — no credible evidence, or evidence of harm. Reserved for compounds with nothing behind them or active red flags.

Where a peptide is strong for one use and weak for another, we grade the best-supported use and say so. The grade is deliberately conservative: it rewards human evidence and discounts mechanism-only hype, which is the opposite of how marketing ranks these compounds.

S grade — approved, trial-proven

Evidence tier: 1 — large human RCTs and regulatory approval.

• Tirzepatide — Grade S · GIP/GLP-1 dual agonist for obesity and diabetes; ~21% weight loss in SURMOUNT-1, approved. See tirzepatide.
• Semaglutide — Grade S · GLP-1 agonist for obesity and diabetes; large STEP and cardiovascular trials, approved. See semaglutide.

These are the only two that meet the regulated-medicine bar, and they're why the whole category gets attention. Everything below this line is a meaningful step down in evidence.

A grade — real trials or approval, narrower scope

Evidence tier: 2 — solid human trials or approval for specific indications.

• Orforglipron — Grade A · oral small-molecule GLP-1 with strong trial data; needle-free, approaching approval. See orforglipron.
• Tesamorelin — Grade A · FDA-approved (Egrifta) for HIV-associated visceral fat; real trial evidence for that use. See tesamorelin.
• Cerebrolysin — Grade A · neurorecovery (stroke, dementia, TBI); multiple RCTs and approval abroad, modest effect sizes. See cerebrolysin.
• PT-141 (bremelanotide) — Grade A · approved (Vyleesi) for hypoactive sexual desire disorder in some women; narrow but real. See PT-141.

These have genuine human evidence, but for specific, often narrow indications rather than the broad claims attached to them.

B grade — promising but not yet proven

Evidence tier: 3 — emerging human plus replicated animal evidence.

• Retatrutide — Grade B · triple agonist with the biggest phase-2 weight loss yet (~24%), but investigational, phase-3 ongoing. See retatrutide.
• CagriSema — Grade B · amylin + GLP-1 combination with trial data, investigational. See CagriSema.
• GHK-Cu — Grade B · best evidence is topical for skin (collagen, barrier); systemic claims are weaker. See GHK-Cu.
• BPC-157 — Grade B · extensive replicated animal data for gut and tendon repair; human trials thin. See BPC-157.
• Sermorelin — Grade B · GHRH analog, historically approved; real pharmacology, limited outcome data. See sermorelin.
• Argireline — Grade B · topical cosmetic peptide with some published wrinkle data. See argireline.
• Tesofensine — Grade B · phase-2 weight-loss trials in humans; development troubled, not approved. See tesofensine.

Real signal here, but the combination of investigational status, narrow evidence, or use-specific limits keeps them out of the top tiers.

C grade — mechanism plus thin human data

Evidence tier: 4 — coherent rationale, sparse or hard-to-evaluate human evidence.

• Semax — Grade C · Russian clinical use for focus/neuroprotection; Western replication thin. See semax.
• Selank — Grade C · Russian anxiolytic data; limited Western evidence. See selank.
• TB-500 — Grade C · thymosin beta-4 fragment for repair; largely animal data. See TB-500.
• CJC-1295 / Ipamorelin — Grade C · GH secretagogues with real pharmacology but limited outcome data, unapproved. See CJC-1295 / Ipamorelin.
• KPV — Grade C · anti-inflammatory tripeptide of interest for IBD and mast-cell activation; mostly preclinical, little human outcome data. See KPV.
• Oxytocin — Grade C · an approved hormone, but the bonding/anxiety/libido biohacking uses are off-label and thinly evidenced. See oxytocin.
• Matrixyl 3000 — Grade C · cosmetic peptide blend with some manufacturer-backed skin data. See Matrixyl 3000.
• SNAP-8 — Grade C · topical cosmetic peptide, limited independent data. See SNAP-8.
• Melanotan-II — Grade C · genuinely causes tanning, but unapproved with real safety concerns that drag the grade down. See Melanotan-II.

These have a plausible basis and sometimes a clear pharmacological effect, but the human evidence is sparse, hard to evaluate, or offset by safety/legality issues.

D grade — mechanism and marketing

Evidence tier: 5 — striking mechanisms, little or no human outcome evidence.

• Dihexa — Grade D · dramatic rodent synaptogenesis, no human outcome data, uncharacterized safety. See dihexa.
• FOXO4-DRI — Grade D · senolytic with mouse data and big anti-aging claims, no human evidence. See FOXO4-DRI.
• P21 — Grade D · preclinical neurogenic peptide, human evidence absent. See P21.
• 5-Amino-1MQ — Grade D · preclinical metabolic target, marketed ahead of human data. See 5-Amino-1MQ.
• AOD-9604 — Grade D · failed to beat placebo for weight loss in human trials. See AOD-9604.

A D isn't a claim these definitely don't work — it's an honest statement that the human evidence needed to know either way doesn't exist (or, for AOD-9604, came back negative). This is where popularity and marketing most outrun the science.

What the grades are not

Evidence tier: 2 — interpretation guidance.

Three things a grade does not mean:

• It's not a recommendation. A high grade rates the evidence, not whether a peptide suits you; an S-grade drug can still be wrong or unsafe for your situation, and requires a prescriber.
• It's not a safety score. Safety is folded in, but the grade primarily tracks evidence strength. A low grade can coexist with real risks (Melanotan-II, LL-37 elsewhere on the site), and a high grade still has its own side-effect profile.
• It's not permanent. Grades move as evidence matures — retatrutide could climb from B to A or S if phase-3 confirms phase-2, and any compound could fall if trials disappoint. We regrade as the data changes.

Read the report card as a map of where the science currently stands, not as a buy list. The grade tells you how much you can trust claims about a peptide; it doesn't tell you to use it.

How does this relate to your evidence tiers?

Evidence tier: 2 — the rubric is a direct mapping.

The letter grades are a consumer-facing front end on the same evidence-tier framework we use throughout the site. The tiers (1–5) are the rigorous, per-claim backbone that our articles cite; the letter grade is the scannable, shareable summary of where a whole peptide lands. S↔Tier 1, A↔Tier 2, B↔Tier 3, C↔Tier 4, D↔Tier 5, with safety and approval nudging the final letter.

The two are designed to work together: if a grade surprises you, the linked peptide page and our tier-by-tier articles show the underlying evidence so you can check our reasoning rather than take the letter on faith. That transparency is the point — a grade you can't interrogate is just another opinion, and the whole value here is that ours is traceable back to the published evidence.

Limitations

This is an evidence-grading editorial, not medical advice or a recommendation to use any peptide.

• A grade rates evidence, not suitability — it is not a recommendation or a safety clearance.
• Grades reflect the best-supported use — a peptide may be weaker for other claimed uses.
• Evidence evolves — grades change as trials report; this is a 2026 snapshot.
• Safety, legality, and sourcing are separate questions covered elsewhere on the site.
• Gray-market sourcing carries real risk regardless of grade — verify via Finnrick.
• Marko Maal, MSc Pharmacy reviewed this article. Reviewer attribution does not constitute a doctor-patient relationship.

The bottom line

Graded honestly by published human evidence, the peptide landscape is top-heavy in attention and bottom-heavy in proof. Only semaglutide and tirzepatide reach S; a small A tier (tesamorelin, cerebrolysin, orforglipron, PT-141) has real trials or approvals for specific uses; most peptides sit at B–C, promising-but-thin or mechanism-plus-sparse-human-data; and several of the most-hyped compounds land at D, where marketing has outrun the science entirely. The grades map directly onto our evidence tiers and link back to the underlying data, so you can check the reasoning. And the central caveat holds throughout: a grade rates the evidence, not whether a peptide is right — or safe — for you.

Related on this site

• Our evidence-tier framework
• GLP-1 complete guide (2026)
• Next-gen multi-agonists overview
• Retatrutide deep dive (2026)
• Peptide stacking: what's safe, what works, what's hype
• Peptide safety & sourcing guide
• What 1,800+ peptide Reddit posts reveal
• All peptides
• Vendor trust-score directory
• Finnrick vendor testing

References

• Wilding JPH, Batterham RL, Calanna S, et al. 2021. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med. 384(11):989-1002. PMID 33567185 — semaglutide (S grade).
• Jastreboff AM, Aronne LJ, Ahmad NN, et al. 2022. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). N Engl J Med. 387(3):205-216. PMID 35658024 — tirzepatide (S grade).
• Jastreboff AM, Kaplan LM, Frías JP, et al. 2023. Triple-hormone-receptor agonist retatrutide for obesity — a phase 2 trial. N Engl J Med. 389(6):514-526. PMID 37366315 — retatrutide (B grade, investigational).
• Bornstein NM, Guekht A, Vester J, et al. 2018. Safety and efficacy of Cerebrolysin in early post-stroke recovery: a meta-analysis of nine RCTs. Neurol Sci. 39(4):629-640. PMID 29245934 — cerebrolysin (A grade).
• U.S. Food and Drug Administration. Approved drug labels (Egrifta/tesamorelin; Vyleesi/bremelanotide). FDA.gov — approval basis for A-grade indications.