A pharmaceutical composition using natural gonadotropin—releasing hormone (GnRH), and/or some of its mimetic peptides, indistinctly bound by its amino or carboxyl extremes to a carrier molecule; in one case by its carboxyl extreme and in the other case by the amino terminal extreme, thus eliciting a faster and more potent immunological response against the endogenous GnRH hormone. This finally leads to the ablation of the GnRH and consequently of the rest of the involved hormones in the stream GnRH/LH-FSH/Testosterone-(estrogens). An advantage of this formulation consists on facilitating the exposition to the immune system of a greater number of epitopes of the GnRH or its mimetics, minimizing thus the steric hindrance produced by the carriers. This invention has a direct application in the castration of pets and animals of economic interest, in the control of human fertility as well as in the treatment of hormone-sensitive tumors, such as that of the prostate, the breast, ovary, the endometry, testicles, hypophysis, salivary glands and other kinds of human tumors.