Quick answer

Few. Across 25 skin trials, hydrolyzed collagen was generally well tolerated, and a review of 15 exercise trials found no adverse effects reported, even at 60 g a day in short studies. The cautions are allergies to the source animal, a rise in urinary oxalate, and protein limits.^1,2,3

Key facts

Fish is one of the nine major food allergens that US labels must name.⁴
30 g of gelatin raised urinary oxalate 43 percent compared with whey protein.³
The main skin trial noted no side effects at 2.5 or 5 g a day.⁵
Most trials used 15 g a day or less.^2,6

What trials reported

Across 25 randomized skin trials, hydrolyzed collagen was generally well tolerated with few adverse events, though the reviewers judged most of the trials likely to be biased.¹

A review of 15 trials of collagen with exercise found no adverse effects reported, including in short studies at 60 g a day, and the main skin trial noted no side effects.^2,5

Most trials used 2.5 to 15 g a day, so there is little information on how 20 g or more a day is tolerated over months.^2,6

Oxalate and kidney stones

Collagen is rich in hydroxyproline, which the body partly turns into oxalate. In a feeding study, 30 g of gelatin raised urinary oxalate 43 percent compared with whey, and 5 to 10 g also changed it, which matters for people who form calcium oxalate kidney stones.³

Hydroxyproline is one of the amino acids that make collagen distinctive. If you have had calcium oxalate kidney stones, ask your doctor before taking collagen every day.³

Allergies

Fish collagen is a concern for people allergic to fish, a major food allergen that labels must name. Some people with alpha-gal syndrome, a red meat allergy usually caused by tick bites, also react to gelatin and other products made from mammals.^4,7

Check the source on the label: bovine (cattle), porcine (pig), marine (fish) or chicken.⁸

If you limit protein

Collagen is protein. If your doctor has set a protein limit, for example because of kidney disease, count collagen toward it.

Medicines

The official sources we checked, NIH and the labels of several common medicines, name no medicine that interacts with collagen. That is not proof of safety, so ask your pharmacist if you take a regular medicine.⁹

Upper limit

No tolerable upper intake level has been set for collagen. Most trials used 2.5 to 15 g a day for up to 12 months, and a review of 15 trials found no adverse effects reported, including in short studies at 60 g a day.^2,10

Who should ask first

Anyone pregnant or nursing, since the trials reviewed here did not include them
Anyone with kidney disease, a history of kidney stones, or a protein limit
Anyone allergic to fish, beef, pork or gelatin, or with alpha-gal syndrome
Anyone with joint pain or swelling that has not been checked by a doctor

Questions people ask

Is collagen safe for women?

The skin trials, almost all in women, reported few adverse events. Pregnant and nursing women were not included, so ask your doctor or midwife first.^1,6

Does collagen affect the kidneys?

No kidney harm was reported in the trials reviewed here. Collagen raises urinary oxalate, which matters if you form kidney stones, and it adds protein, which matters if you have kidney disease and a protein limit.^2,3

Are there side effects for men?

None specific to men were reported. The joint and training trials included men, and no adverse effects were reported in the exercise trials reviewed.^2,11

See what we make

Every product shows its whole label and what its lab report covers. The store opens soon.

See the Full Measure line Collagen Peptides Collagen Peptides

Sources

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.