blind submitted the retatrutide 10 mg to Janoshik, did not say whose it was. 98.7% vs 98.5% claimed. fourth time their number has been the low one
Supplier source file · GSP
GenScript Biotech Corporation
Peptide synthesis house trading as GenScript Peptides (genscriptpeptides.com), based in Nanjing, China — est. 2002, solid-phase synthesis run in house, Janoshik-tested, Medutest, PeptideMeter and VendorInvestigate verified, supplying 350+ peptides, sarms, injectable oils and raw materials with full COA documentation and worldwide tracked shipping.
4.6room score / 5
703member reports
157archive mentions
#8of 22 suppliers
Open the GSP storefront at genscriptpeptides.com →
Straight to the source, in a new tab. The room is paid nothing for it and a link is not a recommendation — it is there so you can read what the company says next to what this page says.
What the room says
A Nanjing solid-phase house rather than a shop that buys finished powder and puts its own label on it, and the difference turns up in what happens when you ask a chemistry question — you get the column, the gradient and the wavelength back instead of a link to the product page. That is most of the case for them here. The certificate carries the method line, the itemised related substances and the water content without being asked, and members who wanted the synthesis record behind a lot got it inside a working day with the lot code in the subject. What #vendor-talk actually argues about is the custom queue: catalogue orders move in hours, bespoke sequences have taken four to five working days just to come back with a number, and people keep planning the second on the timings of the first.
Dispatch & warehouses
Regional stock. Orders leave a warehouse in the member’s own country.
- Netherlands (Rotterdam) — European Union, 2-4 days
- Germany (Hamburg) — Germany, Austria, Switzerland, 2-4 days
- United Kingdom (London) — United Kingdom & Ireland, 2-3 days
- United States (California) — United States, 2-4 days
- Canada (Toronto) — Canada, 3-5 days
- Australia (Melbourne) — Australia & New Zealand, 3-5 days
Consistently praised
- Method line, itemised related substances and water content on the certificate as standard, catalogue orders included
- Assay has landed at or above the certificate on every lot logged since 2025
- Synthesis is in house, so route and coupling questions get answered rather than deflected
Worth knowing before you order
- Custom sequences are quoted individually and the quote itself has taken four to five working days — do not plan a bespoke order on catalogue timings
- Inland dispatch out of Jiangsu, so ask which of your lines is held in regional stock rather than sent from Nanjing
- The certificate carries purity by RP-HPLC with the wavelength, net peptide content, water content and the lot code — the synthesis record comes back on request if you quote the lot
Company facts
| Legal name | GenScript Biotech Corporation |
|---|---|
| Trades as | GSP |
| Also called | GSP, GenScript Peptides, GenScript Biotech |
| Domain | genscriptpeptides.com → |
| City | Nanjing, Jiangsu, China |
| Established | 2002 |
| Independent testing seen | Janoshik, Medutest, PeptideMeter; writeups cross-checked against VendorInvestigate |
Sponsored · paired placement
Direct manufacturerGL Biochem (Shanghai) Ltd. — the synthesis houseFounded 1998. ISO 9001 and cGMP, 1,500+ staff, 200+ patents. A great deal of what gets sent for testing was made here first. Custom synthesis quoted to small orders.Browse GL Biochem →Verification log
Chronological, oldest first. Every row links to the exact message in the archive. Nothing is ever removed from this log, including entries that later turned out to be wrong. If a row raises a question about a catalogue line, the answer is usually one click away: check it against genscriptpeptides.com →
2024-01-07u100_pat — sourcing question i have never had a problem i could not resolve with GSP, which is a low bar and a lot of suppliers fail it, regional…#vendor-talk2024-07-24typosquat_tay — from the quote log is a first order ever the right time to buy more than one thing — and has anyone worked out the actual per mg cost…#vendor-talk2024-11-22VialBot — Verification log updated: GSP — evidence added, status unchanged.#bloodwork2025-04-01VialBot — Purity check: nothing on file for lot A-3115 from GSP. Not a finding.#eu2025-05-25VialBot — Verification log updated: GSP — evidence added, status unchanged.#payments2025-07-04nordic_price_nils — two places, same month my first order from GSP was fine and my fourth was better. they have improved#vendor-talk2025-08-14VialBot — No new results filed for GSP since 2025-04-24.#food-and-training2025-10-07VialBot — Verification log updated: GSP — evidence added, status unchanged.#scam-watch2025-11-12VialBot — Verification log updated: GSP — evidence added, status unchanged.#dosing-titration2025-12-19tenpence — ok so how many suppliers do people keep on rotation and why that number, genuine question GSP answered a lot specific question inside a…#vendor-talk2026-01-31is_this_forever — anyone compared GSP and SWB on the same compound, for my own notes#vendor-talk2026-02-19VialBot — Result note: GSP lot H-3260 recorded at 97.4% by Medutest.#bloodwork2026-03-26back_from_away — per milligram pedantry anyone compared GGPeps and GSP on the same compound, asking because two people told me different things#vendor-talk2026-05-05month_six_me — update from 11 months ago: GSP added evidence and the entry now reflects it, vial, certificate, invoice, report#vendor-verification2026-05-21swab_dry_first — provenance photo attached does GSP being verified mean my vial is fine#vendor-verification2026-06-30assay_not_purity — route report reship policies vary enormously. GSP honoured one for me without being pushed, which is not universal#shipping-customs
Community rating
From 703 member reports logged since 2024. This room's own number, varied independently of any other community's, and never for sale.
Member reviews
ignacio_r★★★★★2026-06-24
santiago_m★★★★★2026-05-30
asked which column the purity ran on and got column, buffer and gradient back in one reply. no upsell bolted onto the answer which i noticed because it never happens
omar_i★★★☆☆2026-05-12
material fine, paperwork fine, but the custom quote took five working days and their catalogue side answers in hours. dont plan a bespoke order on catalogue timings. logging it because i wish someone had told me
nayeli_d★★★★★2026-04-08
karl fischer water content already printed on the cert, unasked. saved me a round trip. small thing, adds up
erez_k★★★★★2026-03-17
day 9 to the UK, tracking updated every hop, customs paperwork right first time which is why it was quick
line_b★★★★☆2026-02-21
nine vials one lot, nine matching codes. one reconstituted with a faint haze that cleared on standing. logging it because i would want to know. n=1
petra_y★★★★★2026-01-15
asked for the synthesis record with the lot code in the subject and had it back inside a working day. did not have to ask twice which is the bar apparently
divya_c★★★★★2025-11-28
second year same line. 98.4% then 98.5% now, same cert layout both times. drift is the thing i watch for and there isnt any
katrin_w★★★★★2025-10-04
related substances itemised with names on them, not "total 0.5%" and good luck working it out. research use only obviously
annika_k★★★★★2026-07-09
lot GSP-26-118. cert matched vial matched invoice. no notes. will order again
kavya_t★★★★☆2025-09-16
all good on the material. marking it down one because the outer box was softer than i want for glass. nothing broke but that was partly luck
cato_va★★★★★2026-04-27
peptide content listed separately from purity. two numbers, correctly separated. it should not be rare and yet
tomas_t★★★★★2025-08-21
first order deliberately tiny to see how a one vial customer gets treated. full document set in the box same as anyone. second order was not tiny
helga_i★★★★★2026-06-02
they quoted a lead time on something two other places just ignored my emails about, then met the date. id rather have a date than an apology
osman_o★★★★★2025-12-11
pulled a cert for an order 13 months old. found it, sent it, no attitude about why i wanted it
anya_d★★★★★2026-03-03
sent one vial to PeptideMeter and one to VendorInvestigate because i did not trust a single number. a tenth of a point apart. fine
saskia_v★★★★★2025-07-19
reconstituted the semaglutide 5 mg and it went clear on contact. no swirl, nothing floating. properly dried cake
kaia_b★★★★☆2026-01-30
vial label print was faint enough that i photographed it before it could wear off. everything else was right. one point off for the label, thats all
runa_aa★★★★★2025-06-25
nine orders across a year, no substitutions, nothing quietly swapped after i paid. boring supplier. highest praise i have
aleksi_ba★★★★★2026-05-18
asked about counter ion, acetate or tfa, got a number with units and the method next to it. one order not a study, saying so up front
isabela_kr★★★★★2025-05-09
cold pack still firm on day 8. someone over there thinks about the box, which is more than i can say for two of their competitors
amira_v★★★★★2026-07-14
Medutest 98.4% on a claimed 98.0%. thats the direction you want that gap pointing. test your own vial anyway, always
Where this supplier comes up
#vendor-talkSupplier experience. Price per mg, lead time, communication, fill consistency.58 mentions#vendor-verificationThe verification log. What counts as evidence and what does not.13 mentions#semaglutideSemaglutide. STEP and SELECT data, 0.25 to 2.4mg, and what happens above it.12 mentions#test-resultsPost the report, the lot number, and where you bought it. One data point is one data point.10 mentions#retatrutideRetatrutide. Triple agonist. Research use only. No long-term safety data.7 mentions#announcementsRead-mostly. Archive changes, verification changes, pinned resource updates.7 mentions#shipping-customsTransit times, declared value, seizure letters, cold packs that arrive warm.6 mentions#coa-readingPurity is not assay. A COA without a lot number is a picture.5 mentions#cagrilintideCagrilintide, amylin analogues, and the combination story.5 mentions#other-peptidesEverything that is not a GLP-1. Evidence standards apply, and they are strict here.5 mentions
Other source files
Where GSP sells
GenScript Biotech Corporation sells from its own storefront. The link is marked nofollow and sponsored and is here so a member can check what this page says against what the company says. The room is paid nothing for it and a link is not a recommendation.
Visit GSP at genscriptpeptides.com →
Whatever the storefront says, check the lot on the vial against the lot on the certificate before you use anything.
Fairness note
Everything on this page is specific and evidenced, and it is written by people who bought the thing. The room keeps its words apart: a shipping question is a shipping question, and fraud is a separate matter dealt with in #scam-watch, which concerns impersonators, lookalike domains and forged certificates rather than any of the twenty-two companies in this directory. Nothing here is medical advice, and research-use-only material is not approved for human use.