Background: 4-MDMB-BUTINACA, a next-generation synthetic cannabinoid, presents significant public health and forensic challenges due to its evolving nature and potential toxicity. Methods: This study evaluates the subacute toxic effects and pharmacokinetics of 4−Fluoro MDMB−BUTINACA (4F-MDMB-BUTINACA) in adult male albino rats, administered orally for seven days at doses of 1 mg/kg, 5 mg/kg, and 15 mg/kg. The hematological, biochemical, and histopathological parameters were assessed and compared to controls. Results: The pharmacokinetics were determined using GC–MS/MS with a positive chemical ionization and granisetron as an internal standard. A histological analysis revealed inflammatory cell aggregation, congestion, hemorrhage, edema, and fibrosis in various tissues, with renal examinations showing tubule degradation, glomerular atrophy, Bowman’s space expansion, edema, and hemorrhage. The liver exhibited cellular infiltration, while cardiac muscle fibers showed myocardial fiber degradation and inflammatory cell aggregation. Biochemical assays indicated significant alterations (p < 0.05) in the serum levels of AST, ALT, ALP, GGT, total protein, albumin, triglycerides, urea, MCHC, MCV, RDW, platelets, neutrophils, eosinophils, and basophils compared to the controls. Conclusions: The validated bioanalytical method revealed rapid absorption of 4F-MDMB-BUTINACA, with a plasma half-life of 2.371 h, a volume of distribution of 2272.85 L, and a plasma clearance rate of 664.241 L/h. In conclusion, 4F-MDMB-BUTINACA is a highly toxic synthetic cannabinoid, particularly affecting the liver, kidneys, and heart.