Cinnamaldehyde, the major active compound in cinnamon oil, has been investigated for its antimicrobial properties. In vitro studies have demonstrated that cinnamaldehyde exhibits activity against a variety of bacteria, including some antibiotic-resistant strains such as Staphylococcus aureus (including MRSA), Escherichia coli, and Pseudomonas aeruginosa. Its mechanism of action is thought to involve disruption of bacterial cell membranes and inhibition of key enzymatic processes. Some studies also show that when used in combination with conventional antibiotics, cinnamaldehyde can have a synergistic effect, enhancing the efficacy of antibiotics and potentially reducing the required antibiotic dose.

However, most of the current evidence is limited to laboratory (in vitro) research. There are very few animal studies and almost no well-controlled human trials evaluating cinnamaldehyde as a stand-alone or adjunctive treatment for bacterial infections. As such, while the scientific rationale for its antimicrobial action is established, clinical effectiveness and safety for use as an alternative or support to antibiotics have not been sufficiently validated. Major regulatory agencies do not currently endorse cinnamaldehyde as a substitute or adjunct for antibiotics in clinical practice. Thus, while the evidence is promising at the laboratory level, it is not yet robust enough for clinical recommendations.