Collagen

What it is

Collagen supplements are made from fish, pig or cattle skin and hides, or from chicken cartilage [1][2]. Common forms are hydrolyzed collagen, specific collagen peptides and undenatured type II collagen. Hydrolyzed collagen doses in trials ranged from 2.5 to 10 g a day [3].

How it might work

Oral hydrolyzed collagen produces measurable blood levels of hydroxyproline and related peptides in healthy adults [1]. That study measured blood levels only, so it does not show that the peptides reach skin, cartilage or bone.

What the research says

Skin: a 2021 meta-analysis of 19 placebo-controlled trials (1,125 people) found better hydration, elasticity and wrinkles over 90 days [4]. A 2025 review of 23 trials found pooled gains, but no effect in high-quality trials or in trials without pharmaceutical funding. Its authors concluded there is currently no clinical evidence to support collagen for skin aging [5]. A 2026 review rated most trials as high risk of bias [6].

Knee osteoarthritis: a 2025 meta-analysis of 11 trials (870 people) found less pain and better function, with high heterogeneity [7]. A 2019 meta-analysis found lower total WOMAC scores, with pain and function subscores not significant [8]. A 2016 trial of 191 people found 40 mg a day of undenatured type II collagen lowered WOMAC scores versus placebo [2]. A 2025 trial of 68 people found no difference from placebo [9]. In athletes with activity-related knee pain, 5 g a day of specific collagen peptides reduced pain during activity [10]. A 2025 trial in 32 people with meniscopathy (meniscus disease) reported pain and quality-of-life gains over eight weeks [11].

Bone: one 12-month trial of 131 postmenopausal women found spine and femoral neck bone density rose more on 5 g a day of specific collagen peptides than on placebo [12]. No meta-analysis of collagen and bone density was found.

Doses used in studies

Hydrolyzed collagen: 2.5 to 10 g a day for 8 to 24 weeks in skin and wound trials [3]. Collagen in skin reviews: a dose range of 1 to 10 g a day, most often 4 g a day [13]. Specific collagen peptides: 5 g a day for 12 months in bone density and 12 weeks in knee pain [12][10]. Undenatured type II collagen: 40 mg a day for 180 days [2].

Safety and interactions

Side effects were low in the reviewed trials [6], and a 2025 knee trial reported none in either group [9]. Collagen supplements are not well regulated for quality, absorption or efficacy [3]. We found no trial data on interactions with medicines, pregnancy, breastfeeding, or people with kidney or liver disease, and no established upper limit.

Caveats and open questions

Funding: most earlier collagen trials were industry-sponsored [9], and the 2025 skin review found benefit only in pharmaceutical-funded trials [5]. Products and doses differ, so results do not transfer between hydrolyzed collagen, peptides and undenatured type II collagen [2][3]. Bone evidence is one trial [12]. A retrospective subgroup analysis of 20 older men who were overweight or obese found a whey- and casein-based blend produced larger muscle and strength gains than a collagen-based blend [14]. A recruiting trial of collagen peptides is listed on ClinicalTrials.gov (NCT05823727).