Collagen: Does It Actually Work?

What Is Collagen?

Collagen is the most abundant protein in your body. It’s the main building block in your skin, bones, cartilage, tendons, and gut lining. Think of it as the glue that holds your body together. Your body makes it naturally, but production starts dropping in your mid-20s and falls faster after 40.

Collagen supplements have been around since the 1980s, but they exploded in popularity over the last decade. They come in a few forms. Hydrolyzed collagen peptides (Types I and III) are the most common. They dissolve in liquids and absorb easily. UC-II (undenatured type II collagen) is a newer option that works through your immune system at much lower doses.

You’ll see collagen marketed for skin, joints, gut health, hair, nails, bones, muscles, and more. Some of those claims hold up. Most don’t. And the biggest problem in collagen research is that the companies selling it are also paying for the studies. We reviewed 53 studies across 9 claims. Here’s what the data actually shows.

The Evidence, Claim by Claim

The sections below break down each claim with real numbers from published meta-analyses and RCTs. Every effect size, confidence interval, and study count comes from peer-reviewed research.

Skin Elasticity and Hydration: Positive Results With a Major Asterisk

Verdict: Maybe | Grade B | 26 studies, 1,721 people

On paper, collagen’s skin data looks impressive. Pu et al. (2023) pooled 26 RCTs with 1,721 people. They found significant improvements in both hydration and elasticity (SMD 0.72, 95% CI: 0.40 to 1.03).

But then Myung (2025) in the American Journal of Medicine took a closer look. They ran a similar analysis with stricter methods. When they removed industry-funded studies, the benefit vanished. When they restricted to high-quality studies only, the benefit vanished again.

Here’s the key number: 18 of 26 studies were industry-funded. Those showed an effect size of 0.89. The 5 independent studies? Just 0.18. That’s a huge gap.

This doesn’t mean collagen definitely doesn’t help your skin. It means we can’t trust the current evidence because too much of it comes from companies with something to sell.

Joint Pain: The Strongest Claim

Verdict: Works | Grade A | 35 studies, 3,165 people

Joint health is where collagen shines. Liang et al. (2024) published in Osteoarthritis and Cartilage with 35 RCTs and 3,165 participants. That’s a lot of data.

Pain reduction: SMD -0.35 (95% CI: -0.48 to -0.22). GRADE rating: Moderate. Function improvement: SMD -0.31 (95% CI: -0.41 to -0.22). GRADE rating: High.

In practical terms, that’s about an 8.5mm drop on a 100mm pain scale. It’s not a miracle, but it’s real and consistent. Trial sequential analysis confirmed there’s enough statistical power to trust these findings. No significant publication bias was detected.

Both hydrolyzed collagen (around 10g daily) and UC-II (40mg daily) showed benefits. UC-II is interesting because you need so much less of it. Safety was clean too. No increase in side effects compared to placebo.

Gut Health: Almost No Evidence

Verdict: No Evidence | Grade D | 1 study, 20 people

This is the claim with the least support. There’s no meta-analysis for collagen and gut health. None.

The only RCT (Taylor 2022) was tiny. Just 20 people. It found no benefit for gut permeability. One uncontrolled study (Abrahams 2022) had a 65% dropout rate. That’s so high you can’t draw any conclusions from it.

And here’s a twist: an animal study found collagen actually worsened colitis in mice. That’s not proof it’ll harm humans, but it’s definitely not encouraging.

If someone’s telling you to take collagen for “leaky gut,” they’re not getting that from research.

Bone Mineral Density: Promising but Complicated

Verdict: Maybe | Grade B | 5 studies, 423 people

Sun (2025) pooled 5 RCTs with 423 postmenopausal women. Collagen peptides increased bone mineral density in the spine and femoral neck (SMD 0.58, 95% CI: 0.12 to 1.04).

The effect looks large on paper. But there’s a problem. Two studies used collagen chelated with calcium, and those showed much bigger effects (SMD 2.34) than collagen peptides alone (SMD 0.51). It’s hard to separate what collagen is doing versus the calcium.

All studies were in postmenopausal women. We can’t say anything about other populations. And the high variation between studies (I2 = 80.1%) means results were inconsistent.

When paired with calcium and vitamin D, benefits were more consistent. But collagen alone? The jury is still out.

Muscle Mass: Real but Overhyped

Verdict: Maybe | Grade B | 8 studies, 418 people

Bischof et al. (2024) pooled 8 RCTs with 418 people. Collagen peptides (15g/day) combined with resistance training increased fat-free mass more than training alone (SMD 0.48, 95% CI: 0.22 to 0.74). No publication bias detected.

That sounds good, but context matters. Every single study combined collagen with 12 weeks of resistance training. You won’t gain muscle just sitting on the couch taking collagen.

Also, 6 of 8 studies used BIA instead of the more accurate DXA for measuring body composition. Most studies came from one research group (the Konig lab), which raises independence concerns. And whey protein still has stronger evidence for muscle building.

Collagen isn’t a bad protein supplement for people who lift weights. But it’s not the best one either.

Wound Healing: Early but Interesting

Verdict: Maybe | Grade C | 3 studies, 240 people

Three RCTs tested oral collagen for wound healing. Two studied pressure ulcers (10-15g/day) and one studied burn wounds (36g/day). All three found collagen improved healing compared to placebo.

But there’s no pooled meta-analysis. The wound types, doses, and durations were too different to combine. The total sample was only 240 people.

The pressure ulcer evidence is the strongest of the three. But with just 3 small studies across different wound types, this is far from proven. It’s promising, not established.

Hair Growth: No Real Evidence

Verdict: No Evidence | Grade D | 0 RCTs testing collagen alone

No RCTs have tested collagen alone for hair growth. Zero.

The few studies that exist used multi-ingredient supplements. One trial showed a 27.6% increase in hair count, but participants took a blend of collagen plus other nutrients. You can’t separate collagen’s effect from the other ingredients.

Any hair benefits you see marketed are based on theory (“collagen supports keratin production”), not human trials. Don’t buy collagen for your hair based on current evidence.

Nail Strength: One Bad Study

Verdict: No Evidence | Grade D | 1 study, 25 people

One open-label study with 25 women found 2.5g collagen peptides increased nail growth by 12% and reduced broken nails by 42% over 24 weeks.

Sounds promising until you learn there was no placebo group and no blinding. That’s a dealbreaker. The placebo effect is strong for subjective outcomes like “my nails feel stronger.”

A small RCT found improvements in nail appearance, but it wasn’t designed to test brittle nails specifically. Until a proper blinded RCT is done, this claim isn’t supported.

Cellulite: One Industry Study

Verdict: No Evidence | Grade D | 1 study, 105 people

One RCT with 105 women found 2.5g/day of VERISOL collagen peptides reduced cellulite by 9% after 6 months in normal-weight women. The effect was smaller (4%) in overweight women.

But this is a single study using one brand-specific product, funded by the manufacturer. No independent replication exists. A 9% improvement in normal-weight women, unreplicated, isn’t enough to recommend buying collagen for cellulite.

Who Should NOT Take Collagen

Most people tolerate collagen fine. Side effects are usually mild: bloating, digestive discomfort, or a bad aftertaste. But there are some important exceptions.

Don’t take collagen if you’re allergic to the source animal. Bovine (cow), marine (fish), and chicken are the most common sources. If you have a fish allergy, don’t take marine collagen.

Be careful with severe kidney disease. Collagen is protein, and 10-15g per serving adds to your daily protein load. Kidneys that aren’t working well can struggle with extra protein.

Watch out for histamine intolerance. Some collagen products contain higher histamine levels, especially marine-sourced ones. If histamine is a problem for you, check the product carefully or choose a different source.

Drug interactions to know about:

• Warfarin: Collagen’s high protein content can reduce warfarin’s effectiveness. Get your INR checked within 1-2 weeks of starting collagen. Keep your intake consistent day to day.
• Tetracyclines and fluoroquinolones: Trace calcium in collagen can reduce antibiotic absorption by 30-90%. Take your antibiotic 2 hours before or 4-6 hours after collagen.
• Bisphosphonates: Protein and trace minerals reduce absorption. Take your bisphosphonate on an empty stomach and wait 60 minutes before taking collagen.
• Levothyroxine: Protein may reduce absorption of thyroid medication. Separate by at least 4 hours.
• Immunosuppressants (UC-II only): UC-II works by modulating immune cells. Combining it with immunosuppressants may block its mechanism or create unpredictable effects. Talk to your doctor first.
• ACE inhibitors: Collagen peptides have mild ACE-inhibitory activity. This may add to blood-pressure-lowering effects. Watch for dizziness.

The Bottom Line

Collagen is a supplement with one strong claim, a few questionable ones, and several that aren’t supported at all.

The joint pain evidence is genuinely solid. 35 RCTs, trial sequential analysis, GRADE ratings of Moderate to High, and no significant publication bias. If you have joint pain or osteoarthritis, collagen is worth trying. Both hydrolyzed collagen (10g/day) and UC-II (40mg/day) have the data behind them.

The skin evidence is the most contested claim in all of supplement research. It looks great in industry-funded studies and falls apart in independent ones. Bone density and muscle mass show promise, but both need more independent research. Gut health, hair, nails, and cellulite don’t have enough evidence to recommend.

If you’re going to try collagen, try it for your joints. That’s where the science actually supports it. For everything else, manage your expectations and know that the marketing is way ahead of the research.