The invention is an epoxy resin based adhesive composition comprising an epoxy resin and a compound comprising an elastomeric prepolymer residue selected from the group of a polyurethane, a polyurea and a polyurea polyurethane having isocyanate end groups, the isocyanate end groups of said prepolymer residue being capped by a capping compound selected from the group consisting of a primary aliphatic, cycloaliphatic, heteroaromatic and araliphatic amine, a secondary aliphatic, cycloaliphatic, aromatic, heteroaromatic and araliphatic amine, a thiol and an alkyl amide, said capping compound being bound to the end of the polymer chain of the elastomeric prepolymer in a manner such that the end to which it is bonded no longer has a reactive group.In addition to the capping compound defined above above, a capping compound selected from the group consisting of a phenol and a polyphenol can be used for capping the isocyanate end groups of the prepolymer residue.