Scientists are warning about the risks posed by paracetamol after it emerged the painkiller had become the leading cause of liver failure in the US. The annual proportion of cases caused by paracetamol - known in the US as acetaminophen - had risen from 28% in 1998 to 51% in 2003, researchers said. The US team found just 20 pills a day - the recommended maximum is eight - was enough to kill, New Scientist reported. Experts said restrictions on sales had helped cut the number of UK cases. Since 1998 in the UK, pharmacies have been advised not to sell more than one pack of 32 paracetamol tablets to any individual.