Misbranded and counterfeit dietary supplements have been an issue on which the US Food and Drug Administration has been vigilantly regulating. The ubiquity of online-shoppable weight-loss supplements and their unrestricted consumption by people with obesity are serious matters of concern. Fucoxanthin, a brown-seaweed-extracted carotenoid has exhibited anti-obesity property in some clinical trials through its ability to over express uncoupling protein (UCP1) in the white adipose tissue, which leads to fat burning. However, since the clinical trials apply pure fucoxanthin instead of fucoxanthin-bearing dietary supplements, a critical analysis is warranted to quantify fucoxanthin in brown seaweeds to validate their rationale in weight loss mechanism. This study examined ten randomly chosen online-sourced brands of fucoxanthin-containing dietary supplements and analyse the content using High-Performance Liquid Chromatography (HPLC) equipped with UV-Vis and photodiode array detector. Our exploration revealed that, of these 10 products, 3 (30%) did not have any detectable quantity of fucoxanthin, 5 (50%) contained a only a trace amount of it, ranging from 0.001-0.01 mg per capsule, and only 2 (20%) products contained 0.4 mg or 2 mg of fucoxanthin, meeting their label claim. This worrying finding may be interpreted that the existing ease-of-access and pervasive nature of online-sourced dietary supplements require more stringent regulatory screening.