Questions about weight loss supplements will come up as the New Year kicks off. Be prepared to talk about some of the most popular ingredients in this category.
Green tea extract is widely used in weight loss products. It contains epigallocatechin gallate (EGCG), which seems to increase calorie and fat metabolism. It also contains caffeine, which is thought to enhance this effect. But clinical research is conflicting. Many studies show that drinking green tea or taking green tea extract that contains about 70-200 mg caffeine and about 576-886 mg catechins (mainly EGCG) daily for 12-24 weeks modestly improves weight loss. But other studies show no benefit. Both green tea as a beverage and extract have been used safely in moderation, but there are concerns about potential liver damage from certain green tea extracts – for example, there’s some evidence that using extracts containing EGCG in amounts greater than or equal to 800 mg daily is linked with a higher incidence of elevated liver enzymes.
Chitosan is another common ingredient. It’s often promoted as a fat blocker. Clinical research shows that taking chitosan 1-3 grams by mouth daily for up to one year may somewhat reduce body weight compared with placebo, but the average weight loss from chitosan in these studies is only 1 kg more than placebo. And it might only help when combined with a calorie-restricted diet. It seems to be well tolerated at a dose of up to 1.35 grams by mouth daily for up to 3 months. But people with a shellfish allergy shouldn’t use chitosan – it’s derived from chitin which is extracted from shellfish.
Berberine, or “Nature’s Ozempic,” is another obvious ingredient in this category. It’s often promoted as a natural alternative to semaglutide (Ozempic) because it seems to increase GLP-1 secretion. But so far, clinical research doesn't show it has the same impact as semaglutide or other GLP-1 agonists. It’s linked to modest improvements in weight loss – taking berberine 300-1500 mg daily for up to 24 months reduces body weight by around 2 kg in people with obesity, but it’s not clear if these effects are significant. And most studies showing potential benefits have been small and of poor quality. Doses up to 1.5 grams daily have been used safely for up to 6 months. But there are drug interactions to watch out for – it moderately inhibits CYP3A4, 2C9, and 2D6.
Remind patients that weight loss supplements are a particularly risky product category in general – they’re notorious for containing undeclared ingredients and stimulants, which can lead to serious adverse effects. Advise caution and remind patients to only choose third party certified products. Dive into our new interactive CE course on Weight Loss Supplements to learn more.
The information in this brief report is intended for informational purposes only, and is meant to help users better understand health concerns. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions. Copyright © 2025 NatMed. Commercial distribution or reproduction prohibited. NatMed is the leading provider of high-quality, evidence-based, clinically-relevant information on natural medicine, dietary supplements, herbs, vitamins, minerals, functional foods, diets, complementary practices, CAM modalities, exercises and medical conditions. Monograph sections include interactions with herbs, drugs, foods and labs, contraindications, depletions, dosing, toxicology, adverse effects, pregnancy and lactation data, synonyms, safety and effectiveness.
