Long-term khat (Catha edulis Forsk.) chewing has negative effects on human body. Khat constituents appear to be capable of disturbing the delicate equilibrium between damaging and protective mechanisms of a cell that is essential for optimal activity, thereby producing oxidative damage. Therefore, the current study was designed to understand the role of khat on cell toxicity, oxidative stability, and inflammation. Khat was extracted using 60% methanol and assessed calorimetrically for its phenolic and flavonoid contents. 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging, oxygen radical absorbance capacity (ORAC), and ferric reducing/antioxidant power (FRAP) assays were used to assess the antioxidant properties. Lipopolysaccharide and interferon gamma induced murine monocytic macrophages cell line (RAW 264.7) were used to assess khat effects on cellular inflammation, oxidative stability, and viability. Khat possesses high content of polyphenols and flavonoids. The results showed a strong potency of antioxidants in DPPH, ORAC, and FRAP assays. Khat decreases the production of the proinflammatory nitric oxide and induces cytotoxicity and reactive oxygen species inhibition. Heavy khat consumption induced-toxicity and symptoms are probably due the harmful effects of its polyphenolic contents.