(a) the prescription must be in writing, must be dated and signed by the medical practitioner, dentist or veterinary surgeon as the case may be, with his or her usual signature and address, and must specify the name and address of the person for whose use the prescription is given, and the total amount of the morphine, cocaine, ecgonine or diamorphine or salt thereof, to be supplied on the prescription, except that in the case of a preparation which is contained in the British Pharmacopoeia and which is not combined with any other preparation or any of the drugs not so contained, it shall be sufficient to state the total amount of the preparation to be supplied. The prescription shall not be given for the use of the prescriber himself or herself;