The invention relates to the use of a sterile aqueous solution of a substance inhibiting the enzymatic decomposition of endogenous opioide neuropeptides, especially enkephalins, for producing a preparation provided for intravenous infusion, in order to intensify the action of punctual stimulation therapy carried out with an electrical current. One such substance is e.g. D-phenylalanine. In cases that are difficult to treat, pain can be effectively reduced or stopped by infusion of the preparation.