Chitosan is a substance made from the shells of various types of shellfish, including shrimp and crabs. While chitosan is sometimes used in plastic surgery to stimulate tissue growth and promote wound healing and by dentists to treat gum disease, it is perhaps best known as a dietary supplement. While scientific studies to prove its efficacy are lacking, chitosan is used by many consumers to treat conditions such as obesity and high cholesterol. Chitosan is available over the counter, without a prescription. Common side effects of chitosan include upset stomach, constipation, and gas. Other potential problems with chitosan consumption include potential drug interactions, triggering a shellfish allergy, and poor absorption of some nutrients.
Chitosan is often consumed before a meal in the hope that it will absorb dietary fat, thus preventing the digestion of fat and its calories. Although its effectiveness as a weight loss treatment has not been proven, many people continue to purchase and use chitosan for that purpose. Some users complain of the most common side effects of chitosan, such as gastric discomfort and gas, although the distress is usually not serious and goes away after a while.
More serious concerns about chitosan side effects include its ability to bind to fat, which can interfere with the absorption of essential minerals, fat-soluble vitamins, and certain medications. Pregnant women in particular are cautioned against the use of chitosan, as it may prevent them from properly absorbing essential nutrients such as vitamins A and D, as well as calcium. Certain medications, such as oral contraceptive pills, are similarly fat-soluble and may be less effective from consuming chitosan. There is also evidence that chitosan increases the effects of warfarin, a blood thinner. Because this interaction could lead to increased bruising or bleeding, warfarin users should avoid chitosan.
Although technically not chitosan side effects, allergic reactions are still a concern for potential chitosan users. Medical writers are careful to note that shellfish allergies are triggered by the meat of a shellfish, not its shell. It's still a good idea for those with shellfish allergies to be wary of chitosan and watch for signs of a shellfish reaction. These symptoms may include swelling, rash, and breathing problems. Because these symptoms can be serious and even life-threatening, chitosan users who experience these symptoms should seek immediate medical attention.