Many dieters prefer natural weight loss aids like chitosan, as they supposedly don’t come with the severe side effects of prescription diet pills. However, don’t make the mistake of assuming these supplements are side effect free. As a fat blocker, chitosan—a sugar found on the outer skeleton of shellfish—causes mild side effects in some users.
Here’s an overview of these side effects and what you can do to treat them.
1. Stomach Upset, Constipation, and Gas
By far the most common chitosan side effects are gastrointestinal. This is because chitosan is indigestible and interrupts fat absorption.
These side effects include nausea, vomiting, cramping, and constipation. Obviously, the higher the fat content in your diet, the worse these side effects become. And, if you currently have a nutrient-absorption disorder, these side effects may be worse.
Similarly, gastrointestinal side effects related to chitosan could be exacerbated in large doses. You can decrease these side effects by talking to your doctor about the right dosage for you. He or she may recommend decreasing chitosan intake or even stop taking it altogether.
If you’re only mildly bothered by these side effects, you might want to try an over-the-counter gas treatment to dispel some of the more embarrassing and uncomfortable gastrointestinal side effects.
2. Possible Shellfish Allergies
Slightly more concerning chitosan side effects may occur in people with shellfish allergies. Because most people with these allergies are allergic to shellfish meat and not the shell itself, these side effects are rare. However, they’re still a possibility.
Allergy-related side effects caused by chitosan include:
- Difficulty breathing
- Chest pain
- Itchiness or skin rash
- Swelling in the lips and tongue
If you develop any of these symptoms while taking chitosan, stop immediately and consult a doctor or allergy specialist.
3. Less Common Side Effects
Rare chitosan side effects include localized swelling, especially in the wrists and ankles. This occurs because chitosan causes blood to clot more rapidly than it would otherwise, causing swelling and bruises in some people.
However, chitosan has the opposite effect in people taking anticoagulants like warfarin. The effects of these blood thinners increase when taken alongside chitosan, which may cause excess bleeding and lightheadedness.
If you take warfarin or other anticoagulants, check with your doctor before taking chitosan.
Using Chitosan Safely
As is the case with any natural supplement, start taking chitosan in a low dosage and watch for potential side effects. Once you’ve assessed tolerance, you can work up to the full recommended chitosan dosage.
If you notice side effects at any point while taking chitosan, it’s a good idea to talk to your doctor. Even if side effects don’t seem serious, it’s important to be careful when it comes to your health.
-  Jull, A.B., C. Mhurchu, D.A. Bennetti, C.A. Dunshea-Mooji, and A. Rodgers. 2008. Chitosan for overweight or obesity. Cochrane database of systematic reviews: 16 July (3).
-  Rohindra, David R., Ashveen V. Nand, and Jagit R. Khurma. Swelling properties of chitosan hydrogels. Department of Chemistry, The University of the South Pacific, Suva, Fiji.