Prolyl-Hydroxyproline
The two-amino-acid fragment of collagen that reaches the blood after gelatin and collagen supplements, and what it does in cells and animals
Prolyl-hydroxyproline (Pro-Hyp) is a dipeptide of proline and hydroxyproline, the commonest pair in collagen. After people eat gelatin, collagen hydrolysate or collagen-rich food, it is the main collagen peptide that turns up in their blood, and it is also released as the body breaks down its own collagen. In cells and animals it starts fibroblast growth, supports cartilage, bone and muscle repair and calms gut and skin inflammation. No study has given Pro-Hyp itself to people.
No established human dose Details ↓
Recommended Dosing
No established human dose
No study we found gave Pro-Hyp itself to people. The human studies gave gelatin, collagen hydrolysate or fish and then measured how much Pro-Hyp appeared in blood or urine, or measured urinary Pro-Hyp as a marker of bone turnover.
What is it?
Collagen is built from repeating triplets that are rich in proline and hydroxyproline, an amino acid found almost only in collagen. When collagen is digested, most of it breaks down to free amino acids, but some short hydroxyproline peptides survive and are absorbed intact. Pro-Hyp is the most plentiful of them. A 2005 study identified it as the main collagen-derived peptide in human blood after volunteers ate gelatin hydrolysates, and later studies found it rising to micromolar levels after plain gelatin as well.
Food is not its only source. The body constantly remodels its own collagen, and Pro-Hyp is the dominant collagen peptide in urine even when people eat little collagen. That is why urinary Pro-Hyp was studied as a bone-turnover marker after menopause, and why its level tracks meat intake less closely than its sister peptide Hyp-Gly does.
In laboratory work Pro-Hyp acts like a signal. It restarts the growth of fibroblasts sitting on collagen, which otherwise stay quiet, and the authors propose this as a way the body links collagen breakdown at a wound to repair. Early experiments disagreed until one group found that standard cell-culture serum already contains Pro-Hyp, masking the effect. It also nudged bone-forming cells to mature through the transcription factor Foxg1, steered stem cells toward cartilage and fat precursors toward beige fat.
In animals, Pro-Hyp itself, not just collagen hydrolysate, has been given by mouth or injection. It protected joint cartilage in mice, improved a leaky skin barrier, sped muscle repair with less scarring after an abdominal wound, reduced colitis more than whole gelatin did, and had an antidepressant-like effect linked to new nerve cells in the hippocampus. A tracer study in rats showed it reaching skin and cartilage, though most of it was chemically modified on the way.
The human trials of collagen supplements, for skin, joints and other uses, tested whole collagen peptide products, not Pro-Hyp alone, and they are covered on the collagen peptides entry. Here the human evidence is measurement: how much Pro-Hyp appears in blood or urine after a meal or supplement, and what urinary Pro-Hyp says about bone. Whether Pro-Hyp is the active part of those supplements in people has not been tested directly.
Mechanism of Action
Pro-Hyp is absorbed intact from digested collagen and also released locally where collagen is remodelled; in cells it acts as a signal rather than as a building block.
Fibroblast growth on collagen
It restarts the growth of fibroblasts attached to collagen, which ignore ordinary growth factors, and draws them out of skin explants.
Bone and cartilage cells
It promotes osteoblast maturation through Foxg1 and, in mice, limits cartilage loss; in stem cells it favours cartilage-type differentiation.
Inflammation
In mice it lowered colon cytokines in colitis and collects in inflamed skin.
Absorbed partly intact
It appears in human blood within hours of eating gelatin; in rats much of it is modified on first pass, but some reaches skin and cartilage intact.
Published Research
These are studies of Pro-Hyp read from their PubMed abstracts: human blood and urine measurements after gelatin, fish and collagen; a urine bone-marker study; studies that gave Pro-Hyp itself to rats and mice; cell work on fibroblasts, bone, cartilage, fat and stem cells; and one review. Trials of whole collagen supplements are on the collagen peptides entry, and two blood studies are under References.
Plain gelatin raises blood Pro-Hyp too
In nine people, eating gelatin raised plasma Pro-Hyp to a peak of about 15.5 nmol/mL two hours later, showing that hydroxyproline-containing peptides reach micromolar levels in blood. A low-molecular-weight gelatin hydrolysate raised Pro-Hyp and Hyp-Gly further, while a standard hydrolysate did not beat gelatin for Hyp-Gly; free hydroxyproline rose less after gelatin than after either hydrolysate.
The main collagen peptide in urine, mostly from the body's own collagen
Of ten collagen peptides measured in 24-hour urine, Pro-Hyp was the most abundant, but it correlated only weakly with meat intake (r = 0.37) compared with Hyp-Gly (r = 0.72). In seven young women, blood Pro-Hyp and Hyp-Gly rose together after a fish meal. Cultured mouse skin released about 1,000 times more Pro-Hyp than Hyp-Gly, pointing to the breakdown of the body's own collagen as Pro-Hyp's main source.
A urine marker of bone turnover after menopause
In 68 postmenopausal women grouped by bone density, the Pro-Hyp dipeptide measured in unhydrolysed morning urine separated osteoporotic women from controls with an area under the ROC curve of 0.90 (sensitivity 0.74, specificity 0.91), did not change with diet, and fell within three months of starting alendronate, earlier than the other resorption markers measured.
Where swallowed Pro-Hyp goes in rats
After rats swallowed radiolabelled Pro-Hyp, radioactivity spread within 30 minutes to many tissues, including skin and joint cartilage, and was taken up by fibroblasts, synovial cells, chondrocytes and bone cells. Most of it had been modified on the proline residue during first pass without the peptide bond being cut; in cartilage about 5% was still intact Pro-Hyp.
Protects joint cartilage in mice
In mice whose joint cartilage was thinned by a high-phosphorus diet, feeding either collagen hydrolysate or Pro-Hyp itself limited the loss of chondrocytes and the thinning of the cartilage layer. In cultured chondrocytes, Pro-Hyp did not change proliferation but held back their turn into mineralising cells, while proline, hydroxyproline and the tripeptide Pro-Hyp-Gly did not.
Improves skin barrier function in hairless mice
Hairless mice fed a magnesium- and zinc-deficient diet develop a leaky skin barrier. Adding Pro-Hyp and Hyp-Gly (0.15% each) to the diet for 35 days lowered transepidermal water loss and raised water content in the outer skin layer, and shifted gene expression in the skin, including muscle-related genes. The two dipeptides were given together, so their effects are not separated.
Antidepressant-like effect in mice
After rats ate a ginger-digested collagen hydrolysate, Pro-Hyp but not Hyp-Gly appeared in their cerebrospinal fluid. Given by mouth to mice, Pro-Hyp reduced immobility in the forced swim test, while Hyp-Gly, proline and hydroxyproline did not; it raised BDNF and nerve growth factor expression in the hippocampus, increased neural progenitor cell proliferation and raised dopamine in the prefrontal cortex.
Pro-Hyp beats whole gelatin against colitis in mice
In mice with dextran sulfate colitis, oral gelatin, glycine and Pro-Hyp, given in the proportions gelatin yields (10:3:0.8 by weight), all helped, with Pro-Hyp the most active. Glycine and Pro-Hyp lowered IL-6 and TNF-alpha in the colon and inflammatory cytokines in the blood, and reduced the rise in white cells, which gelatin did not.
Faster muscle repair with less scar after wounding
In a mouse model where part of the abdominal wall is cut out and heals with a fibrous scar, drinking a low-molecular-weight collagen peptide containing Pro-Hyp and Hyp-Gly advanced muscle regeneration and reduced fibrosis by day 21. To isolate the dipeptide, pure Pro-Hyp was injected into the abdomen daily; it brought differentiating muscle cells into the wound and reduced scar tissue.
Builds up where skin is inflamed
In mice with chronic hapten-induced contact dermatitis of the ear, the inflamed ear held more Pro-Hyp than control ears, while Hyp-Gly stayed low. Four hours after mice swallowed isotope-labelled Pro-Hyp, labelled dipeptide was found in the inflamed ear only, so Pro-Hyp both arises from fast collagen turnover in the lesion and is delivered there from food.
Stimulates hyaluronic acid in joint-lining cells
Pro-Hyp increased hyaluronic acid production by cultured synovium cells, and it appeared in guinea pig blood after the animals ate collagen hydrolysate. In the guinea pig osteoarthritis model the benefit to cartilage was shown for the hydrolysate as a whole, not for Pro-Hyp on its own.
Triggers growth of skin fibroblasts on collagen
Added to serum-free culture, Pro-Hyp increased the number of fibroblasts migrating out of mouse skin discs, an effect blocked by the cell-division inhibitor mitomycin C. Fibroblasts grown on collagen gel normally stop dividing even with serum; Pro-Hyp restored their growth in a dose-dependent way.
Why some labs saw no effect: Pro-Hyp hidden in the serum
Fibroblast results with Pro-Hyp varied between batches of fetal bovine serum. The serum itself turned out to contain about 100 micromolar hydroxyprolyl peptides, Pro-Hyp included, which masked any added effect. After small molecules were stripped from the serum, Pro-Hyp and Hyp-Gly again triggered growth of fibroblasts on collagen and their migration from mouse skin.
Drives bone-cell maturation through Foxg1
In MC3T3-E1 mouse osteoblast-like cells, Pro-Hyp raised alkaline phosphatase activity and the bone genes Runx2 and osterix. Knocking down the transcription factor Foxg1 abolished these effects, while knocking down Foxo1 did not, placing Foxg1 in the pathway.
Nudges rat fat precursors toward beige fat
Rat stromal-vascular cells differentiated with Pro-Hyp in the medium grew at the same rate and stored similar fat, but expressed fewer white-fat markers and more brown-fat markers, including Ucp1, Ucp3 and Dio2, suggesting a shift toward beige adipocytes.
Steers human dental pulp stem cells toward cartilage
In human dental pulp stem cells sorted for the SSEA3 marker, Pro-Hyp and Hyp-Gly both increased proliferation of the SSEA3-positive cells. Pro-Hyp favoured cartilage-type differentiation, with early type II collagen and sustained SOX9 expression and more matrix after two weeks, whereas Hyp-Gly favoured bone-type differentiation.
A growth-starting signal for wound fibroblasts
This review argues that Pro-Hyp, released where collagen is broken down at a wound, starts the growth of a particular set of fibroblasts (those carrying the p75NTR stem-cell marker) that sit on collagen fibres and otherwise ignore protein growth factors. Because eating gelatin or collagen hydrolysate also supplies Pro-Hyp, the authors suggest these supplements could help chronic wounds, a proposal still to be tested.
No Established Human Dose
No study we found gave Pro-Hyp itself to people. The human studies gave gelatin, collagen hydrolysate or fish and then measured how much Pro-Hyp appeared in blood or urine, or measured urinary Pro-Hyp as a marker of bone turnover. The animal studies gave the pure dipeptide, but those amounts do not translate into a human dose. Collagen supplement trials tested whole products and are on the collagen peptides entry.
What this rests on: PMID 34461513, PMID 39458568, PMID 18844493.
Educational information, not medical advice. The doses on this page come from approved labels, published studies and, where no study exists, amounts reported by users. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose. Full medical disclaimer.
What a Buyer Needs to Know
What is sold, how it is mixed, stored and taken, and what is known about its safety, quality and legal status. Each part names its source. Where we have none, it says unknown.
What is sold
Unknown: we hold no label and no published test that says what forms or vial sizes Prolyl-Hydroxyproline is sold in. A vial's own label is a seller's claim, not a source.
Mixing a vial: a worked example
Unknown: no human dose of Prolyl-Hydroxyproline has been established (see No Established Human Dose below), so there is no amount to work out. The reconstitution calculator does the arithmetic for any vial, water and dose.
Storage before and after mixing
Unknown: no label or published stability study on file says how to store Prolyl-Hydroxyproline, before or after mixing. The mixing guide sets out the general rules, with their sources: keep a mixed vial in the fridge, and use it promptly, as the bacteriostatic water label says of any drug dissolved in it. The 28 days often quoted is the limit for an opened multiple-dose vial from a manufacturer, an outer limit set for sterility, not a time a mixed solution has been shown to keep. Nobody has published how long Prolyl-Hydroxyproline stays intact once mixed.
How it is taken
Unknown: with no established human dose, there is no established way of taking Prolyl-Hydroxyproline. What the human studies gave and how is set out under No Established Human Dose.
What to expect, and when
Unknown: no cited half-life and no label or trial duration on this page says how long Prolyl-Hydroxyproline lasts or how long it was given. Results reported in the studies are under Published Research.
Side effects, and when to stop or get help
From the Side Effects section: It is formed naturally when collagen is digested and when the body remodels its own collagen (PMIDs 34461513, 39458568); The animal studies that gave pure Pro-Hyp reported benefits in their models and did not describe harms in their abstracts (PMIDs 19615963, 34548594). Full list and cautions ↓
When to stop or get help: unknown; no label or trial on file sets rules for stopping Prolyl-Hydroxyproline. Treat a severe or unexpected reaction as a reason to stop and see a doctor.
Source: the Side Effects section below (“Pro-Hyp has not been given alone to people, so it has no side effect record of its own”).
Interactions
Unknown: a PubMed search for human interaction studies of Prolyl-Hydroxyproline (reviewed 2026-10-28) found none. Unknown is not the same as safe to combine.
Every peptide's record, with its source: the interaction matrix.
Checking what you bought
Unknown: no published independent test of Prolyl-Hydroxyproline products is in our lab-results database yet, so how products sold under this name measure up is not known.
To read a certificate of analysis, paste it into the COA decoder; it checks the measured mass against Prolyl-Hydroxyproline's expected mass, 228.2 Da, from this entry's molecular data. Trust & Verification explains what independent testing can and cannot show.
Legal status
US: Research Chemical (Not a drug: a dipeptide formed from dietary and body collagen). Sport: Not on the 2026 List.
Country by country ↓ · Regulatory tracker
Source: this entry's approval status and the WADA Prohibited List, as in Legal Status below.
Side Effects & Contraindications
Reported Side Effects
Pro-Hyp has not been given alone to people, so it has no side effect record of its own.
Contraindications & Cautions
There is no Pro-Hyp product with a label.
Legal Status
Pro-Hyp is a dipeptide formed from dietary and body collagen; it is not a medicine.
Frequently Asked Questions
?What is Pro-Hyp?
Prolyl-hydroxyproline, a dipeptide of proline and 4-hydroxyproline. It is the main collagen-derived peptide found in human blood after eating gelatin or collagen hydrolysate.
?Does taking collagen raise Pro-Hyp?
Yes. In volunteers, gelatin and collagen hydrolysates raised plasma Pro-Hyp, peaking about one to two hours after eating. A low-molecular-weight hydrolysate raised it more than gelatin.
?Is Pro-Hyp the active part of collagen supplements?
That is the leading hypothesis. In cells and mice, Pro-Hyp alone reproduced several effects of collagen hydrolysate, but no human trial has given Pro-Hyp on its own to test it.
?Does the body make Pro-Hyp without supplements?
Yes. Breakdown of the body's own collagen releases it, and it is the most abundant collagen peptide in urine even with little collagen in the diet.
?Is there a Pro-Hyp dose?
No. Pro-Hyp has not been given alone to people. Collagen supplement trials used whole products, covered on the collagen peptides entry.
?Is cyclic Pro-Hyp the same thing?
No. Cyclic Pro-Hyp is a ring-closed form (a diketopiperazine) that also appears in blood after collagen hydrolysate, at about a twentieth of the linear form's level in one pilot study.
References
- [other] PubChem CID 11902893, Prolylhydroxyproline: formula C10H16N2O4, molecular weight 228.24. Read October 28, 2026. https://pubchem.ncbi.nlm.nih.gov/compound/11902893
- [pubmed] Iwasaki Y, et al. "Comparison of gelatin and low-molecular weight gelatin hydrolysate ingestion on hydroxyproline (Hyp), Pro-Hyp and Hyp-Gly concentrations in human blood." Food Chem, 2022;369:130869. PMID: 34461513.
- [pubmed] Asai TT, et al. "Hydroxyprolyl-Glycine in 24 H Urine Shows Higher Correlation with Meat Consumption than Prolyl-Hydroxyproline, a Major Collagen Peptide in Urine and Blood." Nutrients, 2024;16(20). PMID: 39458568.
- [pubmed] Husek P, et al. "Prolyl-hydroxyproline dipeptide in non-hydrolyzed morning urine and its value in postmenopausal osteoporosis." Clin Chem Lab Med, 2008;46(10):1391-7. PMID: 18844493.
- [pubmed] Kawaguchi T, et al. "Distribution of prolylhydroxyproline and its metabolites after oral administration in rats." Biol Pharm Bull, 2012;35(3):422-7. PMID: 22382331.
- [pubmed] Nakatani S, et al. "Chondroprotective effect of the bioactive peptide prolyl-hydroxyproline in mouse articular cartilage in vitro and in vivo." Osteoarthritis Cartilage, 2009;17(12):1620-7. PMID: 19615963.
- [pubmed] Shimizu J, et al. "Oral collagen-derived dipeptides, prolyl-hydroxyproline and hydroxyprolyl-glycine, ameliorate skin barrier dysfunction and alter gene expression profiles in the skin." Biochem Biophys Res Commun, 2015;456(2):626-30. PMID: 25498544.
- [pubmed] Nogimura D, et al. "Prolyl-hydroxyproline, a collagen-derived dipeptide, enhances hippocampal cell proliferation, which leads to antidepressant-like effects in mice." FASEB J, 2020;34(4):5715-5723. PMID: 32115749.
- [pubmed] Zhu S, et al. "Gelatin versus its two major degradation products, prolyl-hydroxyproline and glycine, as supportive therapy in experimental colitis in mice." Food Sci Nutr, 2018;6(4):1023-1031. PMID: 29983966.
- [pubmed] Jimi S, et al. "Collagen-derived dipeptide Pro-Hyp administration accelerates muscle regenerative healing accompanied by less scarring after wounding on the abdominal wall in mice." Sci Rep, 2021;11(1):18750. PMID: 34548594.
- [pubmed] Kusubata M, et al. "Detection of endogenous and food-derived collagen dipeptide prolylhydroxyproline (Pro-Hyp) in allergic contact dermatitis-affected mouse ear." Biosci Biotechnol Biochem, 2015;79(8):1356-61. PMID: 25848885.
- [pubmed] Ohara H, et al. "Effects of Pro-Hyp, a collagen hydrolysate-derived peptide, on hyaluronic acid synthesis using in vitro cultured synovium cells and oral ingestion of collagen hydrolysates in a guinea pig model of osteoarthritis." Biosci Biotechnol Biochem, 2010;74(10):2096-9. PMID: 20944430.
- [pubmed] Shigemura Y, et al. "Effect of Prolyl-hydroxyproline (Pro-Hyp), a food-derived collagen peptide in human blood, on growth of fibroblasts from mouse skin." J Agric Food Chem, 2009;57(2):444-9. PMID: 19128041.
- [pubmed] Asai TT, et al. "Food-Derived Collagen Peptides, Prolyl-Hydroxyproline (Pro-Hyp), and Hydroxyprolyl-Glycine (Hyp-Gly) Enhance Growth of Primary Cultured Mouse Skin Fibroblast Using Fetal Bovine Serum Free from Hydroxyprolyl Peptide." Int J Mol Sci, 2019;21(1). PMID: 31905705.
- [pubmed] Kimira Y, et al. "Collagen-derived dipeptide prolyl-hydroxyproline promotes osteogenic differentiation through Foxg1." Cell Mol Biol Lett, 2017;22:27. PMID: 29213293.
- [pubmed] Minaguchi JA, et al. "Remodeling of rat stromal-vascular cells to brite/beige adipocytes by prolyl-hydroxyproline." J Vet Med Sci, 2017;79(3):547-553. PMID: 28123139.
- [pubmed] Suzuki R, et al. "Selective effects of collagen-derived peptides Pro-Hyp and Hyp-Gly on the proliferation and differentiation of SSEA3-positive human dental pulp stem cells." Regen Ther, 2025;29:162-170. PMID: 40170801.
- [review] Sato K, et al. "Collagen-Derived Di-Peptide, Prolylhydroxyproline (Pro-Hyp): A New Low Molecular Weight Growth-Initiating Factor for Specific Fibroblasts Associated With Wound Healing." Front Cell Dev Biol, 2020;8:548975. PMID: 33330443.
- [pubmed] Iwai K, et al. "Identification of food-derived collagen peptides in human blood after oral ingestion of gelatin hydrolysates." J Agric Food Chem, 2005;53(16):6531-6. PMID: 16076145.
- [pubmed] Shigemura Y, et al. "A Pilot Study for the Detection of Cyclic Prolyl-Hydroxyproline (Pro-Hyp) in Human Blood after Ingestion of Collagen Hydrolysate." Nutrients, 2018;10(10). PMID: 30248982.
Sources & Citations
Every study on this page was read from its PubMed record on October 29, 2026. Status comes from Drugs@FDA (openFDA) and EMA's Article 57 product data, read the same day. Grey Peptides sells nothing and links to no vendor.
Medical Disclaimer: This content is for educational and informational purposes only. It is not medical advice, and nothing here is an instruction to obtain or use any compound. Talk to a licensed clinician about your own situation.