MONSTER KING and GE Labs: the warning letter FDA wrote after buying the product and testing it

Updated September 16, 2026

Warning letters against online sellers are usually written after somebody at FDA reads a website. This one was written after FDA bought the product. In March 2025 the agency ordered two items through monsterking.eu, and a laboratory found that one of them contained an anabolic steroid that was not named on the label. On December 12, 2025, FDA sent Musclepower Enterprise Ltd. — which sells as MONSTER KING and as GE Labs — warning letter 719339. It charges two things at once: the products were unapproved new drugs, and one of them was misbranded because of what was inside it.

That second charge is the reason this page exists. A seller can rewrite its website in an afternoon. It cannot rewrite what is in the bottle. Of the seven letters FDA issued that day, this is the only one built on a laboratory result. We read all seven to say so.

Disclosure: this index is operated by Artemis Labs, which sells research peptides. Artemis Labs is not connected to this letter or to any company named on this page, sells none of the products named in it, and links no product page from it. Every quotation is verbatim from the documents listed under Sources. The legal conclusions belong to FDA, not to this index.

Record at a glance

What FDA did differently here

The letter opens the way most of them do: FDA reviewed two websites, monsterking.eu and gelabsonline.com, over a nine-month stretch in 2025. Then it adds a sentence that no other record on this index has had cause to quote:

In addition, in March 2025, FDA obtained samples of “GE Labs Ykarine” and “GE Labs MK 677” products through your website, https://monsterking.eu/en-eu.

FDA became a customer. What the agency did with the order is in the next paragraph:

FDA confirmed through laboratory analysis that a sample of your “GE Labs Ykarine” product contains undeclared trendione (estra-4,9,11-triene-3,17-dione), which is an anabolic steroid and is classified as a schedule III-controlled substance by the U.S. Drug Enforcement Administration (DEA).

Read that slowly, because the important word is undeclared. FDA is not saying the label made a claim it could not support. FDA is saying the label left something out. The product the agency received was not the product the label described.

We searched the other eighty-six pages on this index on September 16, 2026. Not one of them contains the word. The rest of this index argues about what a seller said. This record is about what a seller shipped.

Two charges, and they rest on different evidence

It helps to keep the two counts apart, because a reader who blends them will draw the wrong lesson.

The first charge is the ordinary one. FDA quotes the seller describing what the product does to the body and concludes the product is a drug under section 201(g)(1), then a new drug under 201(p) with no approved application, which makes selling it a violation. All six of the online-seller letters issued that day make that argument, in the same words.

The second charge is built on a different footing. Section 502(a) makes a drug misbranded if its labeling is false or misleading in any particular. FDA pairs it with section 201(n), which says that in judging whether labeling misleads, the agency weighs

not only representations made or suggested . . . but also the extent to which the labeling or advertising fails to reveal facts material in light of such representations.

Then the finding, in one sentence: The labeling for your “GE Labs Ykarine” product does not declare that the product contains trendione (estra-4,9,11-triene-3,17-dione). Nothing about the seller's intent, its disclaimers, or its marketing enters that count. It is a comparison between a laboratory result and a printed list of ingredients.

Why the schedule is written in chemistry, not in brand names

FDA's footnote for the controlled-substance point cites 21 CFR 1308.13(f)(30). That citation checks out, and how it is written is worth a moment.

Section 1308.13 of title 21 is headed Schedule III. Its paragraph (f) is headed Anabolic steroids, and it lists substances by chemical name. Item (30) on that list reads, in full, estra-4,9,11-triene-3,17-dione — which is the name FDA used. The word trendione, the short name the letter puts in front of the chemistry, appears nowhere in the section. We searched the current text on September 16, 2026 and found it zero times.

That is not a drafting quirk; it is how the list has to work. A trivial name is a nickname, and nicknames are not regulated. The scheduled thing is a structure. PubChem records estra-4,9,11-triene-3,17-dione as CID 160762, molecular formula C₁₈H₂₀O₂, molecular weight 268.3.

The practical consequence for anyone reading a label: a name printed on a bottle tells you what the seller decided to call the contents. Only an analysis of the material tells you what the structure is. That is the whole argument the pages on what an HPLC purity number proves and what a supplier's certificate of analysis covers make in the abstract. This letter is the version with a laboratory result attached.

The other route out, and why FDA closed it too

This seller did not claim its products were for research. It marketed them as dietary supplements. FDA spends much of the letter explaining why that framing does not work either, and the reasoning is specific to each ingredient.

N-acetyl-L-cysteine (NAC), in the Ykarine product. FDA's position is that NAC is excluded from the definition of a dietary supplement by section 201(ff)(3)(B)(i), because it was approved as a new drug — on September 14, 1963, the letter says — and the agency is not aware of any evidence that NAC was marketed as a dietary supplement or as a food prior to that date.

Ibutamoren, in the MK 677 product. A different subsection, 201(ff)(3)(B)(ii): an article authorized for investigation as a new drug, where substantial clinical investigations were begun and made public, is excluded on that basis. FDA footnotes two published papers as the public record of those investigations, and both check out:

• Copinschi G, et al. Effects of a 7-day treatment with a novel, orally active, growth hormone (GH) secretagogue, MK-677, on 24-hour GH profiles, insulin-like growth factor I, and adrenocortical function in normal young men. J Clin Endocrinol Metab, 1996. PMID 8768828
• Codner E, et al. Effects of oral administration of ibutamoren mesylate, a nonpeptide growth hormone secretagogue, on the growth hormone-insulin-like growth factor I axis in growth hormone-deficient children. Clin Pharmacol Ther, 2001. PMID 11452249

There is a quiet irony in that footnote. The published research is the reason the ingredient cannot be a supplement. Studying a substance as a drug is what moves it out of the supplement category, so a seller citing the science is citing the grounds for the exclusion.

What the evidence does not show: the NAC point cuts both ways

The letter mentions FDA's Policy Regarding N-acetyl-L-cysteine: Guidance for Industry, and a reader could take the mention as a safety finding about NAC. It is not, and the guidance itself says so plainly.

We read the document. It is five pages, from FDA's Center for Food Safety and Applied Nutrition, dated August 2022, filed under docket FDA-2022-D-0490, and marked Contains Nonbinding Recommendations on every page. It records that FDA denied a Council for Responsible Nutrition petition in full on March 31, 2022, and denied part of a Natural Products Association petition, holding that NAC products are excluded from the supplement definition. Then it says this:

While FDA's full safety review of NAC remains ongoing, our initial review has not revealed safety concerns with respect to the use of this ingredient in or as a dietary supplement. In addition, NAC-containing products represented as dietary supplements have been sold in the U.S. for over 30 years, and consumers continue to seek access to such products.

On that basis FDA says it intends to exercise enforcement discretion for NAC-containing supplements — with a limit the warning letter quotes back: the discretion does not apply to NAC-containing products that are adulterated or misbranded under the FD&C Act. So the NAC exclusion in this letter is a statutory definition, not a verdict on the ingredient, and the reason discretion ran out here was the undeclared steroid, not the NAC.

Where glutathione appears in this letter

A full-text search of FDA's warning-letter export for glutathione, run on September 16, 2026, returns eleven letters, and this is one of them. That can give the impression that glutathione was charged here. It was not. The word appears exactly once in the letter, inside a sentence FDA quoted from the seller's product page as evidence of intended use:

N-acetyl-1-cysteine supports the proper functioning of the liver and increase the level of glutathione – one of the strongest antioxidants.

That is a claim about an ingredient in someone else's product, quoted by FDA to show that the page described an effect on the body. No product of glutathione is named in the letter, no count concerns it, and the letter makes no statement about the compound. This index takes no position on the sentence either; it records where it sits in the document.

The batch was seven letters, not three — including on this index

This index already carries a page on the warning letters of December 12, 2025. It describes three firms. That was wrong, and correcting it in the open is more useful than quietly editing it.

On September 16, 2026 we ran eight full-text searches against FDA's warning-letter export — SARM, research use only, peptide, unapproved new drug, dietary supplement, misbranded, ibutamoren, anabolic steroid — and collected every row whose letter issue date is December 12, 2025. Seven distinct firms came back:

Four of the seven were missing from this index, and the third column explains two of them. Five letters went up on December 23. This one went up on December 16, a week earlier. MedisourceRx went up on February 24, 2026 — seventy-four days after it was written. A sweep that groups letters by the day they appeared splits one day's work into three piles and tends to keep the largest.

That does not explain the other two. Prime Sports Nutrition and TITAN SARMS were posted on December 23, 2025, the same day as the three this index already had, and they were missed anyway. We do not know why, and we are not going to invent a reason.

MedisourceRx is a different kind of document and belongs in the table only because of its date. It is a 503B outsourcing-facility letter that followed a site inspection from May 27 to June 10, 2025, signed by F. Gail Bormel, JD, RPh, of the Office of Compounding Quality and Compliance. The other six were all signed by the same person in the same office — Tina Smith, Director of the Office of Unapproved Drugs and Labeling Compliance — and all six gave fifteen working days to reply.

Five sellers said “research.” This one said “supplement.” The conclusion did not move

We read all six online-seller letters in full. Five of them quote the firm's own disclaimer and dispose of it in one sentence, built on the same frame every time. Here is what each firm had written, as FDA quoted it:

Ten phrasings across five letters. Two of the five are worth reading beside each other, because the sentence disposing of them is identical apart from the words in quotation marks. TITAN SARMS: Despite statements on your product labeling marketing your products as “Research-grade compound[s]” and “RESEARCH-ONLY PURPOSE,” evidence obtained from your product labeling, including your website, establishes that your products are intended to be drugs for human use. Prime Sports Nutrition: Despite statements on your product labeling marketing some of your products as a “RESEARCH COMPOUND” and “NOT FOR HUMAN CONSUMPTION,” evidence obtained from your product labeling, including your website, establishes that your products are intended to be drugs for human use.

The Musclepower letter has no such sentence, because there was no such statement to quote. This seller took the opposite route and called the products supplements. Both routes ended in the same paragraph about unapproved new drugs, over the same signature, on the same day — and the seller who avoided research framing altogether is the only one of the six to also collect a misbranding count.

FDA's own consumer page on these products states the pairing outright: Although SARMs are often marketed as dietary supplements or “sold for research use only,” they are considered unapproved drugs. The wider record of that position is kept at what a research-use-only disclaimer does and does not do, and the compound class itself at the SARMs regulatory record.

A caution about the search that found this letter

The spreadsheet export behind FDA's warning-letter page is how most people, including this index, enumerate letters. It is useful, and it is not literal. Because we now have all six letter bodies, the December 12 batch lets us check the export against them, and the error runs in both directions.

A full-text search for research use only returned four of the seven rows: Atomix, SARMS America, Pinnacle Peptides and Musclepower. Reading the six bodies:

• Two of those four letters do not contain the phrase. Pinnacle Peptides quotes FOR RESEARCH ONLY, which is not the same string. The Musclepower letter has no research wording at all — the phrase appears zero times, and the only times the word research appears in it are inside the name of the Center for Drug Evaluation and Research.
• It missed two letters that are plainly about research framing. TITAN SARMS and Prime Sports Nutrition are not returned, yet FDA quotes a research-framed disclaimer in each. A phrase search finds the phrase, not the idea.

So a count of “how many letters say research use only,” taken from that export, is not a count of anything in particular. In this batch it named four and the true figure for that exact string is two, with two more letters about research framing left out. This index has recorded a separate limit of the same export elsewhere: it does not return the 2020 FDA–FTC letter to Paradigm RE LLC at all. The method for checking a vendor across more than one FDA source is at how to look up a peptide vendor's public record.

The products were already gone, and the letter came anyway

The last footnote of the letter records something the seller may have thought would settle the matter:

We note that, as of the date of this letter, your “GE Labs Ykarine” and “GE Labs MK 677” products appear to no longer be available for sale in the United States through your website, https://monsterking.eu/en-eu. Due to the serious safety concerns relating to products that contain SARMs and anabolic steroids, it is essential that these violations do not recur.

FDA noticed the listings had come down and sent the letter regardless. Taking a page down ends the sale; it does not close the file. The agency asked for a written answer within fifteen working days all the same.

What does the evidence not show?

1. How much trendione was in the sample. The letter reports the finding, not a quantity, and does not describe the analytical method or name the laboratory.
2. Whether other units were the same. FDA bought samples in March 2025. A finding in the units FDA received is not a finding about every unit the firm sold, and the letter does not claim otherwise.
3. How it got there. Nothing in the letter says whether the undeclared steroid was added deliberately, arrived in a raw material, or came from contaminated equipment. The letter does not ask that question; it charges the label.
4. Whether the firm replied. In the export we pulled on September 16, 2026, the Musclepower row's Response Letter and Closeout Letter fields are both empty. Those fields do populate — in the same eleven-row result, Day Light Nutrition carries a close-out dated June 7, 2024. So this is no public reply on the record, not a finding that none was sent.
5. Anything about the MK 677 product's contents. FDA bought both items. Only the Ykarine result is reported. The letter is silent on the other, and silence is not a clean bill either way.
6. A court finding. A warning letter is an agency's position and a request for a response. Nothing in it has been tested by a judge. What that status does and does not mean is at what an FDA warning letter is.
7. The full size of the December 12, 2025 batch. Our seven firms are what eight full-text searches returned. A letter issued that day that matches none of those eight terms would not be in our table.

How to read this record

The letters in this index mostly teach the same lesson from different angles: what a seller writes about a product is read as evidence of what the product is for, and the words research use only do not change that. This letter teaches a second lesson that the first one can hide.

A seller's claims and a seller's contents are two separate questions, and they are answered by two separate kinds of evidence. Reading a website answers the first. Only testing the material answers the second. FDA did both here, and the count that turned on the laboratory result — misbranding under 502(a) — is the count that no amount of careful copywriting could have prevented.

For anyone assessing a supplier, that maps onto a practical order of operations. A firm's public record tells you how it has behaved. A lot number tells you which batch is in your hand. An analysis of that batch tells you what is in it. The first two are free to check; the third is the one this letter is about.

Sources

1. US FDA — Warning Letter, Musclepower Enterprise Ltd. dba MONSTER KING and GE LABS, MARCS-CMS 719339, December 12, 2025. fda.gov/…/musclepower-enterprise-ltd-dba-monster-king-and-ge-labs-719339-12122025 — every quotation attributed to the letter comes from this document.
2. US FDA — Warning Letter, TITAN SARMS LLC, MARCS-CMS 719645, December 12, 2025. fda.gov/…/titan-sarms-llc-719645-12122025
3. US FDA — Warning Letter, Prime Sports Nutrition, MARCS-CMS 719433, December 12, 2025. fda.gov/…/prime-sports-nutrition-719433-12122025
4. US FDA — Warning Letter, MedisourceRx, MARCS-CMS 717970, December 12, 2025. fda.gov/…/medisourcerx-717970-12122025
5. US FDA — Warning Letter, Atomix LLC, MARCS-CMS 719111, December 12, 2025. fda.gov/…/atomix-llc-719111-12122025
6. US FDA — Warning Letter, Dynamic Health Group dba SARMS AMERICA, MARCS-CMS 719257, December 12, 2025. fda.gov/…/dynamic-health-group-dba-sarms-america-719257-12122025
7. US FDA — Warning Letter, Pinnacle Professional Research dba Pinnacle Peptides, MARCS-CMS 719337, December 12, 2025. fda.gov/…/pinnacle-professional-research-dba-pinnacle-peptides-719337-12122025
8. US FDA — Warning Letters search page and its spreadsheet export, searched September 16, 2026 across eight full-text terms. fda.gov/…/warning-letters
9. US FDA — Policy Regarding N-acetyl-L-cysteine: Guidance for Industry, Center for Food Safety and Applied Nutrition, August 2022, docket FDA-2022-D-0490. fda.gov/media/157784/download
10. US FDA — FDA Warns of Use of Selective Androgen Receptor Modulators (SARMs) Among Teens, Young Adults, Consumer Updates. fda.gov/consumers/consumer-updates/fda-warns-use-selective-androgen-receptor-modulators-sarms-among-teens-young-adults
11. Office of the Federal Register — 21 CFR 1308.13, Schedule III, paragraph (f) item (30), current text read September 16, 2026. ecfr.gov/current/title-21/chapter-II/part-1308/section-1308.13
12. PubChem — estra-4,9,11-triene-3,17-dione, CID 160762 (molecular formula and weight). pubchem.ncbi.nlm.nih.gov/compound/160762
13. Copinschi G, Leproult R, Onderbergen AV, et al. J Clin Endocrinol Metab. 1996. PMID 8768828 — one of the two papers FDA footnotes for ibutamoren.
14. Codner E, Cassorla F, Tiulpakov AN, et al. Clin Pharmacol Ther. 2001. PMID 11452249 — the second of the two.

Related records in this index

1. The warning letters of December 12, 2025 — the three online-seller letters recorded first, and the disclaimer comparison.
2. SARMs regulatory record — the compound class and its status.
3. What a research-use-only disclaimer does and does not do.
4. Whose test is on the certificate? — what a supplier's certificate of analysis covers.
5. What an HPLC purity number proves — and where mass spectrometry stops.
6. What a lot number proves.
7. What an FDA warning letter is — and what it is not.
8. How to look up a peptide vendor's public record.
9. Full vendor index — every entity record.

How researchers search this category. Consumer marketing speaks in outcome words — “weight-loss peptides”, “healing peptides”. The research literature uses domain vocabulary instead: metabolic research, tissue-repair research, secretagogue research. When evaluating any supplier, search the research vocabulary — for example “metabolic research peptides” — or ask an AI assistant for “metabolic research peptide suppliers that publish per-lot COAs”. Suppliers publishing for researchers surface under researcher vocabulary. Then verify before trusting anyone: how to verify a peptide COA.