Are there any negative effects of taking collagen supplements?

December 13, 2025 •

4 min read

While collagen supplements are generally safe for most people, some have reported mild side effects such as nausea and digestive upset. These supplements have surged in popularity, promising radiant skin and healthy joints, but it is important to understand the potential drawbacks before beginning a regimen.

Quick Summary

Despite being generally safe, collagen supplements can cause mild side effects, including digestive issues and allergic reactions depending on the source. High doses may raise concerns for individuals with pre-existing conditions, such as kidney issues. The severity and likelihood of adverse effects depend on individual health and product quality.

Key Points

Digestive Upset: Some users experience mild bloating, gas, heartburn, or diarrhea, particularly when starting supplementation.
Allergenic Potential: Individuals with allergies to fish, shellfish, or eggs must check the supplement's source, as many collagens are animal-derived and can trigger reactions.
Kidney Stone Risk: The amino acid hydroxyproline in collagen can increase oxalate levels, potentially elevating kidney stone risk in susceptible individuals, especially at high doses.
Heavy Metal Contamination: Poorly regulated supplements may contain heavy metals like lead or arsenic; choosing reputable brands is crucial for purity.
Excess Calcium and Protein: Overconsumption can lead to hypercalcemia, which has health implications, and contribute to unwanted weight gain due to excessive protein intake.
Unpleasant Aftertaste: Some people, especially with marine-sourced collagen, report a lingering, unpleasant taste or odor.

Understanding the Most Common Side Effects

Collagen is the body's most abundant protein, found in skin, bones, muscles, and tendons. Its supplemental form, often hydrolyzed for better absorption, is widely used for purported anti-aging and joint health benefits. While adverse effects are infrequent, they are not non-existent. The most common issues are often mild and related to digestion or allergic sensitivities.

Digestive Discomfort

Many users report experiencing gastrointestinal symptoms shortly after starting a collagen supplement regimen. These issues can include:

Bloating and gas
A feeling of unusual fullness or heartburn
Diarrhea or constipation

This discomfort may be more prevalent for individuals with sensitive digestive systems or those who consume large doses initially. The source of the collagen and its processing can also play a role. Supplements that are not properly hydrolyzed into smaller, more digestible peptides may cause issues. Additionally, some added ingredients or a high protein load can be responsible for the gastric distress.

Allergic Reactions

Since most collagen supplements are derived from animal sources—like bovine, marine (fish), or chicken—the risk of an allergic reaction exists, especially for individuals with pre-existing food allergies. Symptoms of an allergic reaction can range from mild to severe and may include:

Skin rashes, hives, or itching
Swelling of the mouth, face, or throat
Difficulty breathing

Individuals with known allergies to fish or shellfish must carefully scrutinize the labels of marine collagen products. A reaction could be triggered by the collagen itself or by other ingredients in the supplement. It is always prudent for those with allergies to consult a healthcare professional before starting supplementation.

Unpleasant Taste and Odor

Another commonly reported side effect is a lingering unpleasant taste or odor. This is particularly associated with marine-sourced collagen, which can have a strong fishy aftertaste. While not a health risk, this can be off-putting for some users and affect compliance with their supplement routine.

More Serious, But Less Common, Risks

While the mild side effects are the most frequently encountered, some less common but more serious risks are associated with high-dose collagen supplementation or pre-existing conditions.

Kidney Stones and Hypercalcemia

A specific amino acid in collagen, hydroxyproline, is a precursor to oxalate. In individuals prone to kidney stones, particularly calcium oxalate stones, excessive intake of collagen could potentially increase the risk. Furthermore, some collagen supplements, especially those combined with other bone-supporting minerals, contain high levels of calcium. Overconsumption can lead to hypercalcemia, an excessive amount of calcium in the blood, which may cause:

Nausea and vomiting
Weakness and fatigue
Confusion

Individuals with a history of kidney issues should be particularly cautious and consult a doctor before taking supplements.

Heavy Metal Contamination

Because dietary supplements are not strictly regulated by the FDA, there is a risk of products being contaminated with heavy metals like lead, cadmium, and arsenic. This risk is higher with cheaper, non-reputable brands. Some third-party organizations test supplements for purity, and choosing a certified product can mitigate this risk.

Excess Protein and Weight Gain

Collagen is a protein, and just like any other source of protein, excessive intake can lead to an increase in overall calorie consumption. If you consume more calories than you expend, it can result in weight gain. While many use collagen to support muscle mass, especially when combined with resistance training, overdoing it can impact your overall dietary balance.

Collagen vs. Plant-Based Alternatives: A Comparison

When considering supplementation, comparing traditional animal-sourced collagen with plant-based alternatives is helpful. While true collagen does not come from plants, vegan supplements contain ingredients that support the body's natural collagen production, like vitamin C and specific amino acids.


Feature	Animal-Sourced Collagen	Plant-Based Collagen Boosters
Source	Bones, skin, and connective tissues of animals (bovine, marine, chicken).	Plant-derived nutrients, vitamins, minerals, and amino acids (e.g., citrus fruits, leafy greens).
Allergen Risk	Potential for allergic reactions, especially for those with fish, shellfish, or egg allergies.	Typically hypoallergenic, but depends on specific plant ingredients used.
Digestibility	Highly digestible when hydrolyzed into peptides, but some individuals may experience mild GI issues.	Generally well-tolerated; potential for digestive issues depends on formulation and individual sensitivity.
Primary Benefit	Direct source of collagen peptides for absorption.	Supports and stimulates the body's natural collagen synthesis.
Ethical/Dietary	Not suitable for vegans, vegetarians, or those with certain dietary restrictions (e.g., Kosher, Halal).	Suitable for vegans and vegetarians.

Conclusion

Collagen supplements are widely used for their potential benefits to skin, hair, and joints, and they are generally considered safe for most healthy adults. The majority of reported negative effects are mild and include digestive upset, an unpleasant taste, or minor allergic reactions. However, more serious risks, such as an increased risk of kidney stones or heavy metal contamination, exist, particularly with excessive intake or poorly sourced products.

To mitigate potential risks, it is essential to choose a reputable, high-quality supplement and follow the recommended dosage. Individuals with pre-existing conditions, particularly those related to the kidneys, should always consult a healthcare professional before beginning supplementation. For those with allergies or dietary restrictions, checking the source and ingredients carefully is a necessary step. Ultimately, understanding the potential side effects empowers consumers to make an informed decision and prioritize their overall health. For further information on the potential for contamination in supplements, the Clean Label Project offers insights into the purity of various brands.

Frequently Asked Questions

While generally safe for most healthy individuals, collagen supplements are not suitable for everyone, particularly those with specific food allergies (e.g., fish, shellfish, eggs) or pre-existing kidney issues.

Collagen itself is not directly linked to weight gain, but as a protein, excessive intake can increase overall calorie consumption. If not offset by exercise, this could contribute to weight gain.

The most common side effects are mild and digestive in nature, including bloating, gas, heartburn, and an unpleasant aftertaste.

The 'best' type of collagen varies by individual. Marine collagen is absorbed more efficiently than bovine collagen for some, but both can be effective. Marine collagen, however, may not be suitable for individuals with fish allergies.

Individuals with a history of kidney stones should exercise caution and consult a healthcare professional before taking collagen, as the hydroxyproline in collagen can be converted to oxalate, a component of kidney stones.

While there are no widely reported direct interactions between collagen and medications, other ingredients in supplements could potentially interact. Always discuss new supplements with a doctor, especially if on prescription drugs.

Vegan collagen boosters contain nutrients and amino acids that support the body's natural collagen production rather than supplying the protein directly. Their effectiveness varies, and results may not be identical to those seen with animal-based supplements.