Inventions relate to medicine, biotechnology, genetic engineering and can be used for analgesia. Plasmid DNA for transient expression in mammalian cells is proposed represented by a backbone containing prokaryotic and eukaryotic elements, a fragment providing enhanced capture of the plasmid DNA by cells and a polynucleotide encoding beta-endorphin modified for increasing the affinity for receptors, codon-optimized for expression in mammalian cells. Producer of such plasmid DNA on the basis of a bacterial cell and an analgesic agent based on such plasmid DNA for application in mammals, in particular, humans, are also given. The technical result of the developed plasmid DNA and analgesic based on it use is to increase the controllability of beta-endorphin synthesis exactly, in increasing the efficiency of plasmid DNA from which beta-endorphin is synthesized, and reducing its amount to achieve analgesia, in increasing the duration of analgesia and in expanding the spectrum of analgesic drugs.