What are the side effects of collagen supplements?

What side effects are reported?

Trials of hydrolysed collagen generally describe it as safe, with side effects that are mild and similar to a high-protein drink:

• Digestive: bloating, a heavy or full feeling, mild nausea, loose stools or heartburn, particularly if you start with 15 g or take it on an empty stomach. Starting at 5 g for a week and building up usually fixes it.
• Taste and smell: unflavoured bovine collagen is close to neutral but some people notice a savoury aftertaste in hot drinks; marine collagen can taste fishy.
• Sweetener tolerance (flavoured products): Biogen's flavoured Peptan collagen uses sucralose, and some people get gas or loose stools from sweeteners or sugar alcohols. Unflavoured powders avoid this.

Who should not use it?

• Allergy: avoid marine collagen if you are allergic to fish or shellfish, and bovine collagen if you avoid beef for allergy reasons. Allergic reactions (hives, swelling, breathing difficulty) need urgent medical care.
• Kidney disease: collagen counts as protein. If you have been told to limit protein, discuss it with your doctor or dietitian.
• Pregnancy and breastfeeding: not studied; see collagen in pregnancy.
• Medication: collagen itself has no established interactions in our research files, but blends can include piperine (black-pepper extract), magnesium or vitamin C. Ask a pharmacist if you take regular medicines.

What about contaminants and label risks?

This is where quality, not collagen, is the issue. We found no published South African heavy-metal test data for collagen, and only one product in our research (New Leaf marine collagen) claims heavy-metal testing, without naming the scheme. Consumer Reports' 2025 testing of 23 protein powders found whey and dairy products generally lowest in lead; that does not cover collagen, but it shows why a batch certificate of analysis matters (details).

Labels can also mislead. A listing for one collagen powder in South Africa claimed "FDA approved" and "WADA certified"; neither claim could be verified, and neither is a normal description for a food supplement. Treat "approved" and "certified" wording with scepticism unless you can check it on the certifier's own register.

Is collagen a good protein?

No, and this is not a side effect but a limitation. It lacks tryptophan and is low in leucine, so do not count it as a full protein serving (is collagen a complete protein).

How to reduce your risk

1. Choose a single-ingredient powder with a short label, such as ATP Fitness Hydrolysed Collagen (R950 for 910 g, October 2026) or The Harvest Table Bovine Collagen. ATP's honest trade-off: it is a young brand (2024), unflavoured, and publishes no third-party test results that we found.
2. Start at 5 g and build to 10 g over a week.
3. Stir into a warm drink, or blend into a smoothie, to avoid clumping (hot coffee).
4. Stop and see a doctor if you get hives, swelling, vomiting or persistent pain.

In South Africa most collagen powders are sold as foods or unregistered complementary products. SAHPRA has not registered any complementary medicines yet, so quality assurance depends on the brand.

Under-18s do not need collagen; food protein covers their needs.

Products mentioned