The invention relates to a polyantiseptic antimicrobial pharmaceutical composition for oral use, for the hygiene and treatment of oral diseases of bacterial, mycotic or viral etiology, for over-the-counter sale, without contraindications. Said composition does not contain phenolic or chlorophenolic compounds, and consists of a mixture of hydrogen peroxide, eugenol, natural camphor, zinc sulphate, sodium fluoride, xylitol, cetylpyridinium chloride and excipients. Said formulation is used to deodorise, disinfect, astringe and soothe inflammation of the oral area, avoids the neoformation of bacterial plaque, prevents tooth cavities, inhibits the formation of dental tartar, improves the resistance of teeth to cavities, and treats and prevents oral aphthous ulcers. It is also used to irrigate and treat periodontal bags, fistulae, abcesses, alveolitis, necrosis and pulp gangrene, to help to avoid oral diseases during orthodontic treatments, post-surgery of the mouth and in patients wearing fixed and detachable prostheses, and to relieve, cure or prevent oral diseases in patients undergoing radiotherapy or chemotherapy, hospitalised patients and terminally ill patients. Said composition is also a medicament for protecting the oral health of systemic patients, patients suffering from nutritional, endocrine, haematological, cardiovascular and psychosomatic disorders in addition to physically or mentally weakened patients or patients with genetic or hereditary alterations.