Collagen is the main protein of skin, bone, tendons and cartilage. Supplements are most studied for knee osteoarthritis pain and for skin hydration.
Ask a doctor or pharmacist before you take collagen if one of these applies to you:
Collagen is a family of proteins that strengthen skin, bone, tendons and cartilage.[5] There are at least 28 types; type I makes up over 90% of the collagen in the body, and type II is found mostly in cartilage.[6][7] Supplements contain collagen from cattle, pigs, fish or chicken. Collagen peptides are collagen cut into short pieces with enzymes.[8][9]
Collagen is most studied for bone and joint health and for hair and skin. In osteoarthritis, a 2024 review of 35 trials found a small to moderate drop in pain and better function.[10] For skin, reviews of 19 and 26 trials found better hydration and elasticity, but a 2025 review found no effect in trials not funded by companies.[4][11][12] With strength training, for fitness, a 2024 review of 19 trials found more fat-free mass.[13] For bone density, one 12-month trial found a small rise.[14]
In osteoarthritis trials, collagen caused no more side effects than control, and in skin trials it was generally well tolerated.[10][15] People with a fish allergy may react to fish collagen.[1] Large doses of gelatin raised the oxalate in urine, a concern for people who have had kidney stones.[2] Skin trials enrolled adults aged 20 to 70, and no trial in pregnancy was found in PubMed.[4] Ask a doctor or pharmacist first if one of these applies to you.
Collagen is a family of proteins that strengthen skin, bone, tendons and cartilage.[5] After a dose of hydrolyzed collagen, some short pieces reach the blood intact.[16]
Collagen peptides are short chains of amino acids that makers cut from collagen with enzymes.[8] In healthy volunteers who took 9.4 to 23 g of gelatin hydrolysate, peptides with hydroxyproline, an amino acid typical of collagen, rose in the blood. They peaked after 1 to 2 hours and fell to half of the peak by 4 hours.[16]
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Trials of collagen peptides gave 2.5 to 15 g a day, according to a 2019 analysis.[20] Trials of undenatured type II collagen gave 40 mg a day.[9][19]
No official upper limit for collagen was found. In a 2024 review of 35 trials, collagen products caused no more side effects or dropouts than control.[10] In one study, 30 g of gelatin raised the oxalate in urine by 43% compared with 30 g of whey protein.[2] Ask a doctor or pharmacist first if you have a fish allergy or have had kidney stones.[1][2]
Most studies gave 2,500 to 5,000 mg a day, for 1 to 3 months.
The counts are study groups. A study group is one set of people in a study who took the same dose. One study can have several groups. These are amounts from studies, not advice for you.
31 of 110 study groups took collagen with something else. This shows what studies gave together, not what works together.
What studies used when they gave collagen for one goal, or to a group of people.
Each protocol describes what studies used, for one goal or for one group of people. It is not advice for you: talk to a doctor before you start a supplement.
12 questions in 4 groups. Open one for the short answer; each has its own page with the full answer and sources.
Yes. Collagen is found in food, mostly in meat.[22] Bone broth contains the amino acids of collagen. But broth made to a standard recipe had less hydroxyproline, glycine and proline than a 20 g dose of a collagen supplement. Broths made to other recipes differed a lot.[27] Collagen lacks tryptophan, an essential amino acid, so it is an incomplete protein.[20]
In people with osteoarthritis, collagen eased pain and improved function a little. A 2024 review of 35 trials with 3,165 people rated the effect as small to moderate.[10] In healthy, active people the evidence is weaker: EFSA, the EU food safety authority, did not accept a claim that collagen keeps joints healthy.[28]
Reviews of 19 and 26 trials found better skin hydration and elasticity with collagen peptides.[4][11] But a 2025 review of 23 trials found no effect in the trials not funded by companies and in the high-quality trials.[12]
Trials tested collagen together with exercise training, and the extra effect was small to moderate. A 2024 review of 19 trials with 768 adults found more fat-free mass and a small gain in maximal strength when collagen was added to training. The certainty was moderate for body composition and low for strength.[13] In 53 older men with low muscle mass, 15 g a day during 12 weeks of training added 4.2 kg of fat-free mass, against 2.9 kg with placebo.[25] Collagen did not raise muscle protein building more than other, higher-quality proteins given in the same amount.[29]
One trial found a small rise in bone density. 131 women after menopause with low bone density took 5 g of collagen peptides or placebo a day for 12 months. Bone density of the spine and of the upper thigh bone rose with collagen and stayed about the same with placebo.[14] No review that pooled several bone trials of collagen was found in PubMed, so this result rests on one trial.[14]
The evidence is weak. In a study without a placebo group, 25 people with brittle nails took 2.5 g of collagen peptides a day for 24 weeks. Their nails grew 12% faster and broke 42% less often.[30] For hair, a 2023 trial tested a tablet with 300 mg of fish collagen plus amino acids, iron and selenium, added to hair loss medicines. Hair improved more than with the medicines alone, but the effect of collagen cannot be separated, and two authors work for the company that sells it.[31]
In trials, collagen caused no more side effects than control. A 2024 review of 35 trials found no rise in side effects or dropouts.[10] People with a fish allergy may react to fish collagen, and large doses of gelatin raised the oxalate in urine.[1][2]
It is not known. Collagen contains hydroxyproline, which the body can turn into oxalate, a part of calcium oxalate stones.[2] In one study, 30 g of gelatin raised oxalate in urine by 43% compared with 30 g of whey protein; doses of 1 and 2 g did not change it.[2] In another, 5 men took 30 g a day for 3 days, and oxalate in urine did not change.[3] Neither study counted kidney stones.[2][3]
No trial of collagen supplements in pregnancy or breastfeeding was found in PubMed. The skin trials in a 2021 review enrolled adults aged 20 to 70, and the training trials in a 2024 review healthy adults.[4][13] Ask a doctor or pharmacist before you take collagen while pregnant or breastfeeding.[4]
The body needs vitamin C to make collagen: one step of collagen building depends on it, and a lack of vitamin C causes scurvy, with weak connective tissue.[6] In one small trial, 8 men took gelatin with vitamin C 1 hour before exercise, and 15 g doubled a blood marker of new collagen.[17] Every gelatin dose in that trial contained vitamin C, so the trial cannot show what vitamin C added.[17]
