Garcinia gummi-gutta based food supplements (GFS) are widely commercialized due to their antiobesity activity, which has been mainly attributed to their high content in (−)-hydroxycitric acid [(−)-HCA]. In order to overcome the limitations related to selectivity and sensitivity of the HPLC-UV methods usually employed for the analysis of this compound, a GC–MS method was fully developed for the first time and validated. Water with 0.1 % formic acid was used for the solubilization of (−)-HCA stabilized in the form of salt in GFS. After a drying step, different derivatization solvents were tested and only trifluoroacetic acid (TFA) allowed the complete dissolution of (−)-HCA. Regarding silylation, the best results were obtained by cold dropwise addition of hexamethyldisilazane and subsequent heating at 45 °C for 90 min. After optimizing the chromatographic conditions, the stability of derivatives for 1 month was also assessed. This new methodology was also applied to determine the (−)-HCA content of 12 commercial GFS. Experimental values ranged from 0.86 to 61%. Forty-two percent of the analyzed samples did not meet the (−)-HCA content declared on the label and 2 GFS showed HCA concentrations lower than 10% (0.86 and 6.0%), which puts into question their effectiveness in regulating obesity. One advantage of this new methodology is that it allows the qualitative and quantitative analysis of (−)-HCA in GFS without coelutions with other interfering compounds and it avoids the solubility problems presented by HCA salts. Moreover, the coupling of GC to MS provides more reliable identification of compounds present in GFS. This work is part of the I + D + I projects PID2019-106405 GB-I00 financed by MCIN/ AEI/10.13039/501100011033 and AGL2016- 80475-R, AEI/FEDER, UE, financed by MINECO. The authors would like to thank the Community of Madrid and European funding from FSE and FEDER programs for financial support (project S2018/BAA-4393, AVANSECAL-II-CM). A. Mena-García thanks the Spanish Ministry of Science, Innovation and Universities for an Industrial Doctorate grant (DIN2019-010849/AEI/10.13039/501100011033) awarded to Phar- mactive Biotech Products S.L.U.