Cannabis-based products have gained attention in recent years for their perceived therapeutic benefits (with cannabinoids such as THC and CBD) and widespread availability. However, these products often lack accurate labelling regarding their cannabinoid content. Our study, conducted with products available in Portugal, revealed significant discrepancies between label claims and actual cannabinoid compositions. A fully validated method was developed for the characterisation of different products acquired from pharmacies and street shops (beverages, herbal samples, oils, and cosmetic products) using high-performance liquid chromatography coupled with a diode array detector. Linearity ranged from 0.4 to 100 µg/mL (0.04–10 µg/mg) (THC, 8-THC, CBD, CBG, CBDA, CBGA), 0.1–100 µg/mL (0.01–10 µg/mg) (CBN), 0.4–250 µg/mL (0.04–25 µg/mg) (THCA-A), and 0.8–100 µg/mL (0.08–10 µg/mg) (CBCA). Among sampled beverages, none contained detectable cannabinoids, despite suggestive packaging. Similarly, oils often differed from the declared cannabinoid compositions, with some containing significantly higher CBD concentrations than labelled. These inconsistencies raise serious concerns regarding consumer safety and informed decision-making. Moreover, our findings underscore the need for stringent regulation and standardised testing protocols to ensure the accuracy and safety of cannabis-based products.