President Donald Trump has imposed a 100 per cent tariff on some pharmaceuticals manufactured outside the US, potentially a heavy blow for one of Australia's biggest exports to the country.Trump signed the order overnight, but it won't take effect for some months.The forthcoming tariff will apply to imports of patented drugs and their active ingredients, in an effort to pressure foreign manufacturers to move their production to the US and negotiate agreements to sell their medicines directly to Americans.LIVE UPDATES: