Best PT-141 Vendors for Research (April 2026)

Across 27 PT-141 vendors and 96 independent Finnrick tests through April 17, 2026, purity ranged 96–99.95%. Almost everyone passes. Quantity accuracy spanned -46% underfill to +72% overfill. Purity is not the differentiator. Dose is.

Most PT-141 roundups cover one vendor in depth or stay generic across peptide categories. This list ranks the seven best PT-141 vendors by confidence in independent batch data, sample depth multiplied by score consistency, not by affiliate rates. Two are A-rated keepers. Two are cautionary entries that prove why 99% purity on a COA means nothing if the vial contains 50% more peptide than the label claims.

The 2026 landscape reshuffled the category. Peptide Sciences, formerly the #1-rated PT-141 vendor (Finnrick avg 9.1, A-rated), voluntarily closed March 6, 2026. Any site still selling under that name is fraudulent. Four GLP-1 vendors received FDA warning letters December 10, 2024 (SwissChems, Prime Peptides, Xcel Peptides, Summit Research). Amino Asylum's warehouse was raided in June 2025.

PT-141 (bremelanotide) is FDA-approved only as Vyleesi for premenopausal women with HSDD (June 2019). All research-chemical PT-141 is unapproved for human use. This list is a research-market quality ranking, not medical advice, not an endorsement of use.

Seven vendors worth knowing about, ordered by how much batch-level evidence backs them.

1. Peptidology: Tightest Quantity Accuracy in the Dataset

Peptidology posts the tightest fill-weight spread of any vendor in the 27-vendor Finnrick dataset. Four independent batches, 9.8/10 average, quantity band of -4.6% to +3.0%.

Finnrick data:

• Average score: 9.8/10 across 4 tests
• Quantity accuracy: -4.6% to +3.0% (tightest spread in dataset)
• Purity: 99.67% to 99.93%
• Batch ID: 01-072-PD
• Grade: A

Practical meaning: a 10mg labeled vial contains 9.54mg to 10.30mg of actual PT-141. Reconstituted with 2mL bacteriostatic water at the standard 5mg/mL dilution, a 0.20mL draw delivers between 0.954mg and 1.030mg. Every draw lands within 5% of a target 1mg dose without mental adjustment. For researchers titrating micro-doses (250–500mcg), that 5% band is the difference between a reproducible protocol and chasing noise.

What to watch:

• Sample depth is 4 tests, good but not deep; watch Q2 2026 batches for drift
• Verify the batch ID on the COA matches the lot stamped on the vial
• Cross-check purity and quantity, not purity alone
• Lot 01-072-PD is the most-tested batch; newer lots should be verified independently

• Best for: Researchers who want default-grade PT-141 without comparing spreadsheets
• Skip if: You need the absolute lowest price per mg (see Polaris)
• Consider if: You are coming off Peptide Sciences (closed March 6, 2026) and need a direct replacement

2. Bulk Peptide Supply: Highest Per-Test Score, Endotoxin Below LOQ

Bulk Peptide Supply has the highest per-test score in the Finnrick PT-141 set and the cleanest endotoxin data. The sample is small, which is the whole caveat.

Finnrick data:

• Average score: 9.9/10 across 2 tests (tentative, small N)
• Quantity accuracy: -0.6% to -0.3% (narrowest deviation in dataset)
• Purity: 99.83% to 99.90%
• Endotoxin: below LOQ (limit of quantification)
• Grade: A (tentative)

Practical meaning: a 10mg vial contains 9.94 to 9.97mg. That is essentially label-accurate, tighter than any other vendor on this list. Endotoxin below LOQ means no measurable bacterial contamination markers at the lab's detection threshold, which matters for sterility-sensitive research protocols. Most vendors do not publish endotoxin data at all, which makes the Bulk Peptide Supply COA unusually complete for the price tier.

What to watch:

• Only 2 Finnrick tests; sample depth is a real weakness
• No public batch history; request COA per order
• Rating could shift once 4+ batches are tested

• Best for: Researchers who weight per-test data quality over sample depth
• Skip if: You require 4+ independent batches before trusting a vendor
• Consider if: Comparing against Peptidology and want a second A-rated option for cross-reference

3. Qing Li Peptide: Deepest Recent Sample, But Watch the Spread

Qing Li Peptide has the freshest and deepest recent testing window in the dataset. Six tests, most recent March 18, 2026. The tradeoff is variance.

Finnrick data:

• Average score: 8.3/10 across 6 tests
• Quantity accuracy: -30.2% to +10%
• Purity: 99.24% to 99.95%
• Most recent test: March 18, 2026 (newest data in entire 27-vendor dataset)
• Grade: A

Practical meaning: a 10mg vial could contain 6.98mg to 11.00mg depending on batch. At the low end, a 0.20mL draw from a 5mg/mL reconstitution delivers 0.70mg instead of target 1.0mg, a 30% underdose. At the high end, the same draw delivers 1.10mg. Purity stays strong across that range, so the upstream synthesis is fine. The fill step is not.

What to watch:

• Ask for specific batch COA before ordering, not a generic one
• Recent 2026 batches have trended tighter than the -30.2% historical outlier
• Verify quantity and purity on every COA
• Sample depth of 6 tests beats every vendor except HK Peptides (7); the data is real, the variance is the story

• Best for: Researchers willing to vet per-batch COAs and adjust dose based on actual quantity
• Skip if: You want to default-trust the label without checking each batch
• Consider if: You need the freshest available data and accept batch-level variance as a tradeoff

4. Polaris Peptides: Cheapest A-Rated Option, But Systematic Underfilling

Polaris is the cheapest A-rated vendor in the dataset and the most consistent underfiller. Six tests, all below label, none above. That is a pattern, not a run of bad luck.

Finnrick data:

• Average score: 7.4/10 across 6 tests
• Quantity accuracy: -2.7% to -14.0% (ALL samples underfilled; no overfill observed)
• Purity: 99.28% to 99.94%
• Price: $30 per 10mg vial ($3.00/mg); $40 per 15mg vial ($2.67/mg)
• Grade: A

Practical meaning: at the worst observed batch (-14%), a 10mg vial contains 8.6mg. Reconstituted to the stated 5mg/mL, actual concentration is 4.3mg/mL, so a 0.20mL draw delivers 0.86mg instead of 1.0mg. Effective price per delivered mg is $3.10 to $3.48, still cheapest in A tier, but the spread is narrower than the label suggests. The 15mg vial at $40 remains the best mg-per-dollar option on the list even after the underfill adjustment.

What to watch:

• Systematic underfill across 6 batches is a manufacturing fill-line bias, not random error
• Adjust expected dose downward by roughly 8% as a working assumption
• Purity is consistently strong (99.28–99.94%); this is a fill-weight problem, not a synthesis problem

• Best for: Cost-sensitive researchers who account for the 8% underfill bias
• Skip if: You need label accuracy without mental-math adjustments
• Consider if: You are stacking multiple peptides and cumulative price spread matters more than per-vial precision

5. Verified Peptides: Grade B, Consistent Overfill Pattern

Verified Peptides is the mirror of Polaris. Strong purity, consistent overfill, and a grade drop to B because the direction of the bias matters for dose-sensitive work.

Finnrick data:

• Average score: 6.5/10 across 4 tests
• Quantity accuracy: +8.9% to +12.2% (ALL samples overfilled)
• Purity: strong across batches (99%+ band)
• Grade: B

Practical meaning: a 10mg labeled vial contains 10.89 to 11.22mg. Reconstituted to the stated 5mg/mL, actual concentration is 5.45 to 5.61mg/mL. A 0.20mL draw delivers 1.09 to 1.12mg against an intended 1.0mg. PT-141 side effects are dose-dependent: nausea at roughly 40%, flushing at roughly 20%, transient BP rise of 2–6 mmHg. A 10% overshoot sits inside the noise for a full-session dose and outside it for anyone titrating micro-doses.

What to watch:

• Consistent overfill is manufacturing bias, same class of issue as Polaris in the opposite direction
• Adjust expected dose upward by roughly 10% if dosing from label
• Better: reconstitute and calculate from actual vial weight with a precision scale
• Overfill pattern has held across 4 tests; treat it as a fixed offset, not a fluctuation

• Best for: Researchers who use full vials per session and do not titrate micro-doses
• Skip if: You are dose-sensitive to side effects (nausea, transient BP rise)
• Consider if: A-rated vendors are out of stock and you need continuity of supply

6. HK Peptides: Cautionary Entry, High Purity, Extreme Quantity Swings

HK Peptides publishes clean purity COAs and fails on fill weight. Seven batches, purity consistently above 99.7%, quantity swinging from -12% to +72%. The variance is the vendor's signature.

Finnrick data:

• Average score: 7.5/10 across 7 tests (deep sample)
• Quantity accuracy: -12.1% to +72%
• Purity: 99.70% to 99.95%
• Most recent: March 2026, 17.2mg in a 10mg-labeled vial
• Grade: D

Practical meaning: reconstitute a 10mg-labeled HK vial with 2mL BAC water expecting 5mg/mL, but the vial actually contains 17.2mg, and actual concentration is 8.6mg/mL. A 0.20mL draw intended to deliver 1.0mg instead delivers 1.72mg, essentially the full FDA-approved Vyleesi dose (1.75mg) in a single injection. A researcher who thinks they are microdosing at 500mcg (0.10mL) is actually at 860mcg. With variance this wide, gravimetric verification per vial is the only way to know what is in the product.

What to watch:

• 7 tests is a deep sample; the variance is the vendor's signature, not bad luck
• High purity COAs from HK Peptides are real and do not address the fill-weight problem
• Clearest illustration of why “published COA” alone is insufficient

• Best for: Nothing in April 2026; the variance is too wide for research protocols
• Skip if: You are running any protocol that requires dose consistency
• Consider if: Never, without gravimetric verification of each vial

7. Peptide Gurus: Grade E, 99%+ Purity, +51–56% Overfill

Peptide Gurus is the textbook case for why purity is necessary but not sufficient. Three tests, purity over 99% on every one, quantity 50%+ over label on every one.

Finnrick data:

• Average score: 3.0/10 across 3 tests
• Purity: 99.15% to 99.31%
• Quantity accuracy: +51% to +56% (ALL samples)
• Grade: E

Practical meaning: a 10mg-labeled vial contains 15.1 to 15.6mg of real PT-141. Reconstituted to the stated 5mg/mL with 2mL BAC water, actual concentration is 7.55 to 7.80mg/mL. A 0.20mL draw intended to deliver 1.0mg delivers 1.51 to 1.56mg, essentially the full FDA-approved Vyleesi dose (1.75mg) in every injection. A researcher titrating toward 500mcg (0.10mL draw) is actually at 755 to 780mcg. Side-effect frequency scales with dose: at 1.5mg+, expect the nausea rate closer to 40% rather than the lower numbers cited for sub-1mg exposure.

What to watch:

• The purity score is real; the problem is the second number on the COA
• Archetype for “published COA does not mean accurate product”
• Across 27 vendors, purity ranges 96–99.95%; the differentiator is always quantity

• Best for: Nothing in April 2026; the overfill is dangerous for dose-titration work
• Skip if: You rely on label accuracy for any reason
• Consider if: You want a textbook case study of why COA purity is necessary but not sufficient

8. How to Use This List: A Practical Checklist

The list ranks vendors by data confidence, but a vendor's average rating does not tell you what is in the specific vial on your desk. Three-step verification to run per order.

Step 1, confirm the vendor is still operating (2026 reality check):

• Peptide Sciences closed March 6, 2026; any site still using the name is fraudulent
• FDA issued warning letters December 10, 2024 to SwissChems, Prime Peptides, Xcel Peptides, Summit Research
• Amino Asylum warehouse was raided June 2025
• Check the vendor's live homepage and Trustpilot recency before paying

Step 2, pull the COA for your specific batch, not a generic sample:

• Request the COA matching your vial's lot number, not the vendor's sample COA
• Ascension Peptides, Core Peptides, and Biotech Peptides publish COAs but have no Finnrick batch data in the April 2026 dataset; they may be fine, but you cannot verify against independent testing
• Shanghai Sigma Audley fraud pattern: impersonator sites publishing real-vendor COAs; verify the COA URL is on the vendor's actual domain

Step 3, cross-check purity AND quantity:

• Purity: 99%+ is the floor, not the ceiling
• Quantity: verify the COA reports fill weight or mg content, not just purity percentage
• If the COA does not list quantity, treat it as missing data; that alone is a red flag

Full methodology in our COA verification guide and live vendor status in our vendor directory. For vendors across all compounds, see our best peptide company ranking.

FAQ

Is PT-141 legal to buy in the US?

Bremelanotide is FDA-approved only as Vyleesi (prescription, June 2019, premenopausal HSDD in women). Research-market PT-141 sold as “not for human consumption” operates in a gray zone, legal to sell as a research chemical but not to market for human use. FDA enforcement has escalated: December 10, 2024 warning letters to four GLP-1 vendors, June 2025 Amino Asylum raid, March 2026 voluntary closure of Peptide Sciences. State-level restrictions are moving faster than federal ones.

How do I reconstitute a 10mg PT-141 vial?

Standard protocol: a 10mg lyophilized vial plus 2mL bacteriostatic water equals 5mg/mL. A 0.20mL draw (20 units on a 100-unit insulin syringe) delivers 1.0mg. A 0.10mL draw delivers 500mcg. Stability is 30 days refrigerated once reconstituted; never freeze after reconstitution. Lyophilized powder stores 1+ year at –20°C. If the vendor underfills or overfills, actual concentration deviates from 5mg/mL.

Why isn't Peptide Sciences on this list?

Peptide Sciences was Finnrick's #1-rated PT-141 vendor (9.1 average, A-grade) through early 2026. They voluntarily closed March 6, 2026. Any website currently using the Peptide Sciences name is fraudulent, typically an impersonator using the brand's lingering search equity. Researchers previously defaulting to Peptide Sciences have two direct replacements on this list: Peptidology for tightest quantity accuracy, Bulk Peptide Supply for highest per-test score.

How does Finnrick PT-141 testing work, and why weight it over vendor COAs?

Finnrick purchases vials anonymously from vendors, then tests both purity (HPLC) and quantity (gravimetric fill-weight analysis), the same metrics as vendor COAs, without the vendor controlling which batch goes to the lab. Across 96 tests, purity ranged 96–99.95%, near-universal pass. Quantity ranged -46% to +72%. That gap is why independent testing matters: vendor COAs can be accurate on paper and still not predict what is in your specific vial.

Is PT-141 the same as Vyleesi?

Same molecule, bremelanotide acetate, a synthetic cyclic heptapeptide and melanocortin-4 receptor (MC4R) agonist. Vyleesi is the FDA-approved brand, manufactured under cGMP for premenopausal women with HSDD at a 1.75mg subcutaneous dose. Research-market PT-141 is the same compound produced outside the FDA-approved supply chain, with the quality spectrum shown in this list's data. Mechanism is identical. Quality and dose accuracy are not.

How does PT-141 differ from sildenafil or tadalafil?

Sildenafil (Viagra) and tadalafil (Cialis) are PDE5 inhibitors, working peripherally on vascular smooth muscle by preventing cGMP breakdown. PT-141 works centrally on melanocortin-4 receptors in the hypothalamus and limbic system, upstream of the vascular response. Onset for PT-141 is 30–60 minutes; duration 6–12 hours. Side effect profiles differ: PT-141 shows nausea in roughly 40%, flushing in roughly 20%, and transient BP rise of 2–6 mmHg; PDE5s cluster around headache, flushing, and hypotension.

Which PT-141 vendor should I default to in April 2026?

Peptidology, based on current Finnrick data. Four independent batches, 9.8/10 average, quantity accuracy -4.6% to +3.0% (tightest in the 27-vendor dataset), purity 99.67–99.93%, batch traceability via lot 01-072-PD. Bulk Peptide Supply scores higher per-test (9.9/10) but has only two tests on record. For cost-sensitive buyers who accept the 8% underfill bias, Polaris at $3.00/mg is the cheapest A-rated option on the list.