Why do I feel weird after taking collagen peptides?

November 7, 2025 •

4 min read

According to user anecdotes and some research, mild digestive issues are among the most common side effects reported by some people after starting collagen peptides. This "weird" feeling often leaves users questioning if their supplement is doing more harm than good and what is causing the reaction.

Quick Summary

Several factors can cause an unusual feeling after taking collagen peptides, including digestive discomfort, allergic reactions to the protein source, issues with product additives, and sensitivities to dosages or quality. These symptoms are generally mild, but paying attention to your body's response is key to determining the cause.

Key Points

Digestive Adjustment: The most common cause is a mild digestive upset, such as bloating, gas, or changes in bowel movements, as your system adjusts to the new protein source.
Allergen Sensitivity: An allergic reaction to the collagen's source (bovine, marine, chicken) or other additives in the product can trigger symptoms.
Dosage and Quality: Taking too high a dose initially or using a supplement with poorly hydrolyzed collagen (less bioavailable) can overwhelm your digestive system.
Hydration is Key: Insufficient water intake when supplementing with high-protein powders like collagen can contribute to constipation and digestive discomfort.
Added Ingredients: Other ingredients like sweeteners, flavorings, or contaminants in low-quality products could be the root cause of your symptoms.
Potential for Headaches: A small subset of users may experience headaches or dizziness, which can be linked to changes in calcium levels, particularly with certain supplement types.

For many, collagen peptides are a staple in their wellness routine, promising benefits for skin, hair, and joint health. However, a small but notable percentage of people report a general feeling of being "off" or "weird" after beginning supplementation. This vague description can encompass a range of symptoms, from mild digestive upset to headaches or a change in mood. Understanding the potential culprits is the first step toward finding a solution and continuing your wellness journey safely.

Digestive Issues and Gastrointestinal Sensitivity

One of the most common explanations for a weird feeling is an issue with digestion. When you introduce a new supplement, especially a concentrated protein, your body needs time to adjust.

Bloating and Gas: Some individuals, particularly when taking larger doses, experience bloating and gas. This can happen because the digestive tract is not yet efficient at breaking down the new protein source. The speed and method of absorption play a significant role here, and slower digestion can lead to increased gas production in the gut.
Constipation or Diarrhea: Changes in bowel habits are also reported. For some, a lack of enough fluid and fiber alongside a high protein intake can lead to constipation. For others, the sudden change can trigger diarrhea. Proper hydration is crucial to help the body process the new protein effectively.
Heartburn: Heartburn is another potential symptom, possibly related to the supplement's effects on stomach acidity. If you experience this, try taking your supplement with food rather than on an empty stomach to see if it lessens the discomfort.

Allergic Reactions and Ingredient Sensitivities

While generally rare, allergic reactions or sensitivities to ingredients can cause a variety of symptoms that contribute to a "weird" feeling. The source of the collagen is a key factor here.

Source Allergies: Collagen peptides are often sourced from bovine (cow), marine (fish), or chicken. If you have a known allergy to any of these sources, you could experience a reaction. Marine collagen, in particular, poses a risk for those with fish or shellfish allergies.
Additives and Contaminants: Many collagen supplements contain additional ingredients like flavorings, sweeteners, or preservatives. A reaction might not be to the collagen itself but to one of these additives. Furthermore, sourcing and manufacturing practices can introduce contaminants, so choosing a high-quality product from a transparent brand is important.

Hormonal and Other Physiological Changes

Beyond digestive and allergic issues, other physiological shifts in the body can cause a sense of unease or change.

Headaches and Dizziness: Some users report experiencing headaches or dizziness. This could be linked to changes in blood pressure or calcium levels, especially with supplements from certain sources that may contain high calcium.
Serotonin Levels: Some studies and anecdotal reports suggest that the amino acid profile of certain collagen peptides, which are low in the amino acid tryptophan, could potentially affect serotonin levels and mood in sensitive individuals. While the evidence is limited, it's worth noting if you experience mood changes.

Quality and Type of Collagen

Not all collagen supplements are created equal, and the manufacturing process significantly impacts how your body reacts to them. The level of hydrolyzation, which breaks down the collagen into smaller peptides, determines how easily your body can absorb it. A poorly hydrolyzed product can be harder to digest, leading to discomfort.

Taking Control: What You Can Do

Reduce your dose: Start with a smaller amount and gradually increase to the recommended serving size. This allows your body to adapt slowly.
Change your timing: Try taking the supplement with a meal instead of on an empty stomach to see if that reduces digestive upset.
Try a different source: If you are using bovine collagen, switch to a marine or chicken-based product, or vice-versa, to rule out a source-specific allergy.
Choose a different type: Opt for a product that is fully hydrolyzed, as this is easier for the body to absorb. Look for supplements with lower Dalton (Da) molecular weights, ideally 3,000 Da or less.
Stay hydrated: Drinking plenty of water is essential for your body to process the extra protein effectively and can help with digestive issues like constipation.
Switch brands: Look for reputable brands that provide third-party testing and are transparent about their ingredients.

Comparison of Collagen Sources and Potential Side Effects


Feature	Bovine Collagen	Marine Collagen	Chicken Collagen	Eggshell Membrane Collagen
Primary Source	Cows (hides, bones)	Fish (scales, skin)	Chicken (cartilage, sternum)	Eggshell membranes
Common Types	Type I & III	Type I	Type II	Type I, V & X
Allergy Risk	Higher for those with beef sensitivities.	Risk for fish/shellfish allergy sufferers.	Risk for chicken or poultry allergy.	Risk for egg allergy sufferers.
Typical Use	Skin, bones, joints.	Skin, hair, nails.	Cartilage, joint support.	Joints, connective tissue.
Potential Issues	Mild digestive upset.	Mild digestive upset, fishy aftertaste.	Less common reports, but possible joint discomfort.	Less common, may cause mild digestive issues.
Bioavailability	Good, especially hydrolyzed versions.	Very high absorption rate.	Good, especially hydrolyzed versions.	Good, unique profile.

Conclusion

Feeling weird after taking collagen peptides is not uncommon, but the cause is often manageable. Pinpointing whether the issue is digestive, an allergic reaction, or a problem with the product's quality is the key to finding a solution. By adjusting dosage, changing the timing of your supplement, or exploring a different source or brand, you can often alleviate the symptoms. However, it is crucial to listen to your body and consult with a healthcare professional if symptoms persist or worsen, especially if you experience signs of a serious allergic reaction. By approaching your supplementation thoughtfully, you can reap the benefits of collagen without the unwanted side effects.

Frequently Asked Questions

Common side effects, while generally mild, include digestive issues like bloating, gas, heartburn, and changes in bowel habits (constipation or diarrhea). Some may also experience a bad taste in their mouth, headaches, or rare allergic reactions.

Yes, in some cases, collagen supplements have been anecdotally linked to headaches or dizziness. This can sometimes be related to the source of the collagen or an increase in calcium levels from supplements derived from marine sources.

Yes, it is possible to have an allergic reaction if you are sensitive to the animal source of the collagen (e.g., bovine, marine, chicken). Symptoms can range from hives and rashes to swelling or breathing difficulties, and you should seek medical attention if severe.

Start with a lower dose and gradually increase it, ensuring you stay well-hydrated throughout the day. You can also try taking it with food rather than on an empty stomach. Choose a high-quality, fully hydrolyzed product to improve digestibility.

Check the ingredients list carefully, as additives like artificial sweeteners, flavors, or fillers can be the cause of your symptoms, rather than the collagen itself. Consider switching to a product with minimal ingredients.

Yes, the source and type of collagen can matter. For instance, marine collagen might trigger a reaction in someone with a fish allergy, while bovine collagen could affect those sensitive to beef. The level of hydrolyzation also affects digestibility.

You should stop taking collagen and consult a doctor if you experience persistent or worsening digestive problems, skin issues, or any symptoms suggestive of an allergic reaction, such as swelling or difficulty breathing.