Molecular conductors such as tetrathiafulvalene–tetracyanoquinodimethane (TTF·TCNQ) are of interest for applications in biomedical devices. In this context, toxicity data should be available. Although separate TTF and TCNQ toxicity studies were reported, that of TTF·TCNQ had not been investigated, mainly because of its low solubility in biological media. Recently, the preparation of TTF·TCNQ in the presence of octylamine (OA), acting as a growth controller, afforded soluble nanoparticles (NPs). These particles can further host a biologically active species, for example, trans-decenoic acid (TRANS). In order to study the integration of TTF·TCNQ-based NPs into biomedical devices, we prepared and studied the cytotoxicity of TTF·TCNQ-OA and TTF·TCNQ-OA@TRANS NPs because (i) the chemical nature of TTF and TCNQ is different in separate compounds (neutral molecules) and the adduct (charged molecules), and (ii) nanomaterials may show cell toxicity. The collected data provide evidence that TTF·TCNQ-OA and TTF·TCNQ-OA@TRANS NPs do not induce cell death in normal cells, human dermal fibroblasts, and cancer cells, HCT-116, for concentrations up to 50 μg mL−1, but do induce an arrest in cell division at a concentration of 100 μg mL−1. These data are encouraging for the use of these TTF·TCNQ-based NPs in biomedical devices.