Covalent conjugation of polyethylene glycol (PEG) molecules to biopharmaceutical molecules is known to increase the pharmacological and medicinal characteristics of proteins and other big molecules and has been utilized effectively in 12 authorized medications. PEG reagents with straight and branched chains up to 40 kDa were utilized with a variety of PEG derivatives with varied linker chemistries. This article discusses the characteristics of PEG, the history and evolution of  PEGylation chemistry, and examples of PEGylated pharmaceuticals with a proven track record. They prefer to employ bigger PEG polymers and complicated PEG structures, although they use extremely pure and well-characterized PEG reagents. The preclinical toxicity data for PEG in PEGylated biologics that have been authorized are summarised. Microscopically detected cell vacuolization in phagocytes, which is connected to the biological function of absorption and elimination of particles and macromolecules from blood and tissues. It's possible. Side effects in toxicity tests typically relate to the active moiety of the medicine, not the PEG moiety, according to experience with commercially available PEGylated pharmaceuticals.