A polymer solution comprising: a biocompatible and biodegradable polymer, in which the biocompatible and biodegradable polymer is selected from the group consisting of poly (d, lactic acid), poly (l-lactic acid) or poly (glycolic acid) , or a copolymer of poly (d, l-lactic acid) or poly (l-lactic acid) and poly (glycolic acid), or polycaprolactone, or a copolymer of caprolactone with lactide and glycolide, or a copolymer of lactide and glycolide with polyethylene glycol, poly (d, l-lactic acid) with polyethylene glycol, and polyanhydride； at least one nucleophilic ingredient, wherein the nucleophilic ingredient is leupropid acetate or octreotide acetate, and an amount of an acid additive such that the polymer of the formulation is less susceptible to the reduction of molecular weight compared to the formulation without the acid additive, and wherein the acid additive comprises one or more acids having a pKa of 5.0 or less, said acids being selected from the group consisting of acetic acid, propanoic acid, glycolic acid, glyceric acid, lactic acid, carboxy-terminated lactic acid oligomers, carboxy-terminated glycolic acid oligomers or the combination of these acids in any ratio having a molecular weight not greater than 1000, and wherein the amount of acid additive is from 2% to 50% in polymer weightUna solución de polímero que comprende: un polímero biocompatible y biodegradable, en la que el polímero biocompatible y biodegradable se selecciona entre el grupo que consiste en poli(ácido d,lláctico), poli(ácido l-láctico) o poli (ácido glicólico), o un copolímero de poli(ácido d,l-láctico) o poli(ácido l-láctico) y poli(ácido glicólico), o policaprolactona, o un copolímero de caprolactona con láctido y glicólido, o un copolímero de láctido y glicólido con polietilenglicol, poli(ácido d,l-láctico) con polietilenglicol, y polianhídrido； al menos un ingrediente nucleofílico, en donde el ingrediente nucleofílico es acetato de leuprólida o acetato de octreótido, y una cant
