Ginkgolic acids and urushiols are natural alkylphenols known for their mutagenic, carcinogenic and genotoxic potential. However, the mechanism of toxicity of these compounds has not been thoroughly elucidated so far. Considering that the SIRT inhibitory potential of anacardic acids has been hypothesized by in silico techniques, we herein demonstrated through both in vitro and computational methods that structurally related compounds such as ginkgolic acids and urushiols are able to modulate SIRT activity. Moreover, their SIRT inhibitory profile and cytotoxicity were comparable to sirtinol, a non-specific SIRT inhibitor (SIRT1 and SIRT2), and different from EX-527, a SIRT1 specific inhibitor. This is the first report on the SIRT inhibition of ginkgolic acids and urushiols. The results reported here are in line with previously observed effects on the induction of apoptosis by this class of compounds, and the non-specific SIRT inhibition is suggested as a new mechanism for their in vitro cytotoxicity.