Member States shall prohibit: (a) the placing on the market of stilbenes, stilbene derivatives, their salts and esters and thyrostatic substances for administering to animals of all species; (b) the placing on the market of beta-agonists for administering to animals the flesh and products of which are intended for human consumption for purposes other than the administering for therapeutic purposes and for zootechnical treatment. Member States shall also prohibit: (a) the administering to a farm or aquaculture animal of substances having a thyrostatic, oestrogenic, androgenic or gestagenic action and of beta-agonists; (b) the holding, except under official control, of animals referred to in (a) their placing on the market or slaughter for human consumption. Member States shall ensure that at the time of the import, manufacture, storage, distribution, sale and use of the substances referred to in Articles 2 and 3 their possession is restricted to the persons authorized by national legislation. Third countries whose legislation authorizes the placing on the market and administration of such substances to animals of all species may not appear on any of the lists of countries from which Member States are authorized to import animals or meat or products obtained from such animals.