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Collagen Supplements: What the Trials Show for Skin, Joints, Hair and Bones

Collagen supplements help a little at most. For knee osteoarthritis, pooled trials found slightly less pain and better function (grade B). For skin, pooled trials looked positive, but trials without company funding, and the high-quality trials, found no effect on wrinkles, elasticity or hydration (grade C). Evidence for bones, hair and nails is thin (grade C to D). Collagen is an incomplete protein, can raise urine oxalate, and fish-based products can cause reactions in people with fish allergy.

Published How we grade evidenceEditorial policy

Collagen is the main structural protein in skin, cartilage, tendons and bone. Supplements sell it as collagen peptides (collagen broken into small pieces, also called hydrolysed collagen), as gelatin, or as undenatured type II collagen, which is taken in milligram amounts. This guide covers adults.

The short version

  • Osteoarthritis (mostly knee): collagen products of several kinds eased pain and improved function a little in pooled trials. Grade B (Liang 2024).
  • Skin: pooled trials looked positive, but trials without company funding, and the high-quality trials, found no effect. Grade C (Myung 2025).
  • Bones: one trial of 131 women found a small rise in bone density; it measured bone scans, not fractures. Grade C (König 2018).
  • Muscle: whey protein built more muscle than collagen in a head-to-head trial. Grade C (Jacinto 2022).
  • Nails: one open study of 25 people, with no comparison group. Grade D (Hexsel 2017).
UseWhat trials foundSize of effectGrade
Osteoarthritis pain (mostly knee)Less pain, better functionSmallB
Skin hydration, elasticity, wrinklesPositive in company-funded trials (all three) and, for elasticity only, in lower-quality trialsNone in trials without company funding or in high-quality trialsC
Bone density after menopauseSmall rise in one main trialSmallC
Muscle with strength trainingSome gain; whey did betterSmallC
Hair thickness (one low-molecular-weight peptide)Thicker hair shafts in one trialSize unclearC
NailsFaster growth in one uncontrolled studyUnclearD

Does collagen help your skin?

Grade C: the benefit disappears in the independent trials. A 2025 meta-analysis pooled 23 randomized trials (1,474 people). Taken together, collagen improved skin hydration, elasticity and wrinkles. But when the authors split the trials by who paid for them, company-funded trials showed benefits and trials without company funding showed none, for all three measures. The high-quality trials also found no effect. The authors' verdict: nothing in the clinical evidence shows that collagen slows or reverses skin aging (Myung 2025).

Reviews that did not split trials by funding were kinder. Pooling 26 trials (1,721 people) found better hydration and elasticity, though the authors flagged several biases in the trials (Pu 2023). A 2026 review of 25 trials found improvements in most of them, but rated most of the trials at high risk of bias (Bassila 2026). Our collagen page and skin health page show B for skin; with the independent trials finding nothing, the evidence fits C.

Does collagen help joint pain or knee arthritis?

Grade B for a small effect in osteoarthritis. Pooling 25 trials (2,856 people), collagen products eased pain a little (moderate certainty) and improved function a little (high certainty), with no more side effects than control (Liang 2024). A smaller pooling of 4 collagen peptide trials (507 people) also found less pain, though all 4 trials carried a high risk of bias (Lin 2023). The products in these pools differed, so no single dose stands out. Our joint pain guide compares collagen with glucosamine, fish oil and turmeric.

Undenatured type II collagen: grade C. In 191 people with knee osteoarthritis, 40 mg a day for 180 days lowered pain and stiffness scores more than placebo and more than glucosamine with chondroitin (Lugo 2016). A 2018 review rated its short-term pain effect as statistically clear but of uncertain clinical size, and its medium-term effect as clinically important (Liu 2018).

Sore joints in active people: grade C. In 147 college athletes (97 analysed), 10 g of collagen hydrolysate a day for 24 weeks eased joint pain slightly more than placebo (Clark 2008). In 139 athletes whose knees hurt during sport, 5 g a day for 12 weeks cut activity pain a little more than placebo, a difference that only just reached significance (Zdzieblik 2017).

Does collagen help your bones?

Grade C: a small rise in bone density, no fracture data. In 131 women past menopause with low bone density, 5 g a day of collagen peptides over 12 months raised spine and hip (femoral neck) bone density slightly against placebo (König 2018). In 51 women with thinning bones (osteopenia), adding 5 g of collagen for 12 months on top of calcium and vitamin D raised shin bone mineral content more than calcium and vitamin D alone (Lampropoulou-Adamidou 2022). Over 6 months, menopausal women given collagen showed no change in bone blood markers (Duangjai 2025). A 2025 pooling found higher bone density overall, but results varied widely between trials (Sun 2025). Collagen is not a substitute for bone medicine; see which supplements help bone density?

Does collagen build muscle?

Grade C. Pooling 19 studies (768 adults who trained), collagen peptides added a little fat-free mass (moderate certainty) and strength (low certainty) (Bischof 2024). But in 22 young adults on a 10-week strength program, whey protein grew muscle more than the same amount of collagen with matched leucine, an amino acid that drives muscle building (Jacinto 2022), and in 25 young men, 15 g of collagen twice a day for a week did not raise muscle-building rates (Kirmse 2024). Our collagen page shows B for muscle; with whey ahead and strength gains at low certainty, the evidence fits C. Our body composition guide covers the trials and who paid for them.

Does collagen help hair or nails?

Hair: grade C. In 114 women aged 20 to 50 who felt their hair was thinning, 1,000 mg of small-fragment (low-molecular-weight) collagen peptides daily for 24 weeks went with thicker hair shafts, and more women on collagen than on placebo had measurable thickening (Hwang 2026). That trial did not count hair loss; see our hair loss guide.

Nails: grade D. In an open study of 25 people with brittle nails, with no placebo group, 2.5 g a day for 24 weeks went with 12% faster nail growth and 42% fewer broken nails (Hexsel 2017).

Biotin vs collagen: neither has strong evidence for hair or nails in people who aren't deficient, and high-dose biotin can throw off lab tests. See does biotin affect thyroid and troponin tests?

Does collagen help gut health or "leaky gut"?

No human trials have tested collagen for gut health, "leaky gut" (a loosely defined idea that the gut lining lets too much through) or digestion, so it is ungraded.

When should you take collagen, and with vitamin C?

Timing has not been tested, so morning or night is your choice. Gelatin before exercise: grade D. In 8 healthy men who took vitamin C-enriched gelatin and, an hour later, skipped rope, it doubled a blood marker of collagen building compared with placebo (Shaw 2017). Vitamin C was not tested on its own, and no trial has compared collagen with and without vitamin C.

What we'd skip

  • Collagen for skin aging: no effect in independently funded or high-quality trials (Myung 2025).
  • Collagen in place of other protein for muscle: whey did better (Jacinto 2022), and collagen lacks tryptophan, an essential amino acid, so it counts as an incomplete protein (Paul 2019).
  • Collagen in place of osteoporosis medicine: trials measured bone scans, not fractures (König 2018).

Safety and interactions

  • Side effects: in osteoarthritis trials, people on collagen had no more side effects or dropouts than on control (Liang 2024); one small pooling found a borderline rise in side effects, at very low certainty (Lin 2023).
  • Kidney stones: collagen contains hydroxyproline, which the body turns partly into oxalate. When volunteers swapped 30 g of whey for 30 g of gelatin, their urine oxalate rose 43% (Knight 2006). If you've had calcium oxalate stones or have kidney disease, ask first; see supplements and your kidneys.
  • Allergy: collagen comes from cow, pig, fish or chicken sources, so if you have a food allergy, check the source on the label. Of 101 people already allergic to fish, 21% were sensitized to fish collagen on testing (Kalic 2020). Some people with alpha-gal syndrome, a red meat allergy that follows tick bites, need to avoid gelatin and other mammal-derived products (Platts-Mills 2020).
  • Interactions: no studies have tested collagen with common medicines, including blood thinners, statins, levothyroxine or metformin. Ask your pharmacist if you take several; see also supplements and blood thinners.
  • Quality: for purity and contaminants, see how to choose a quality supplement.

When to see a doctor

  • A knee that is hot, red or badly swollen, locks or gives way, or hurts after an injury.
  • A bone that breaks after a minor fall, or a diagnosis of osteoporosis.
  • Hives, lip or throat swelling, or trouble breathing after a collagen product: get emergency help.
  • Sudden hair shedding or brittle nails with tiredness: ask for blood tests, including iron; see our iron supplements guide.

Don't stop a prescribed medicine on your own; ask the prescriber or pharmacist. If you are pregnant or breastfeeding, ask your midwife or obstetric team; see supplements while breastfeeding. If you are under 18, ask a clinician.

FAQ

Does collagen actually work? For knee osteoarthritis pain, pooled trials found a small benefit (grade B). For skin, the gains seen overall vanished in trials without company funding and in high-quality trials (grade C). Evidence for bones, and for hair (one small-fragment peptide product), is thin (grade C), and for nails thinner still (grade D).

What is the best time to take collagen? Timing has not been tested, so take it whenever suits you.

Is collagen better than whey protein for muscle? No. In 22 young adults on a 10-week strength program, whey grew muscle more than collagen matched for leucine, and collagen is an incomplete protein.

Is collagen safe for your kidneys? In volunteers, 30 g of gelatin raised urine oxalate by 43% compared with whey, which matters if you form calcium oxalate stones. With kidney disease or past stones, ask your clinician first.

Can I take collagen with blood thinners or other medicines? No studies have tested collagen with common medicines. Ask your pharmacist.

Sources

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  2. Myung SK, et al. Effects of Collagen Supplements on Skin Aging: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Am J Med. 2025. PubMed 40324552 · doi:10.1016/j.amjmed.2025.04.034
  3. König D, et al. Specific Collagen Peptides Improve Bone Mineral Density and Bone Markers in Postmenopausal Women-A Randomized Controlled Study. Nutrients. 2018. PubMed 29337906 · doi:10.3390/nu10010097
  4. Jacinto JL, et al. Whey Protein Supplementation Is Superior to Leucine-Matched Collagen Peptides to Increase Muscle Thickness During a 10-Week Resistance Training Program in Untrained Young Adults. Int J Sport Nutr Exerc Metab. 2022. PubMed 35042187 · doi:10.1123/ijsnem.2021-0265
  5. Hexsel D, et al. Oral supplementation with specific bioactive collagen peptides improves nail growth and reduces symptoms of brittle nails. J Cosmet Dermatol. 2017. PubMed 28786550 · doi:10.1111/jocd.12393
  6. Pu SY, et al. Effects of Oral Collagen for Skin Anti-Aging: A Systematic Review and Meta-Analysis. Nutrients. 2023. PubMed 37432180 · doi:10.3390/nu15092080
  7. Bassila C, et al. Efficacy and safety of hydrolyzed collagen supplementation on skin health outcomes: a systematic literature review of randomized controlled trials. Eur J Clin Nutr. 2026. PubMed 42342959 · doi:10.1038/s41430-026-01778-3
  8. Lin CR, et al. Analgesic efficacy of collagen peptide in knee osteoarthritis: a meta-analysis of randomized controlled trials. J Orthop Surg Res. 2023. PubMed 37717022 · doi:10.1186/s13018-023-04182-w
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  10. Liu X, et al. Dietary supplements for treating osteoarthritis: a systematic review and meta-analysis. Br J Sports Med. 2018. PubMed 29018060 · doi:10.1136/bjsports-2016-097333
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