We carried out an investigation with the purpose to evaluate the real concentration of coumarin by high performance liquid chromatography with diode array detector (HPLCDAD) in some guaco syrups and associations (Mikania glomerata Spreng.), marketed in Sao Paulo, Brazil. At first, we developed some analytical method parameters and then we investigated the quality of nine commercial syrups, purchased in pharmacies, compounding pharmacy and another in a house of Northeast herbals, called “lambedor of guaco, composed of natural herbs”. We also carried out an investigation about package and drug label of the studied products, according to ANVISA standardization. The most syrups samples have a lower coumarin concentration than those recommended by ANVISA as a minimum daily dose. Regarding to packaging and drug label, many of them are complies with the current legislation, while others are in a complete disagreement. Despite the importance of this plant species for the Brazilian herbal medicine, including those belonging to the official list of the Unified Health System, many efforts are still needed to offer to the Brazilian population adequate quality products. Therefore, it is necessary a better supervision about quality control of phytomedicines.