Sometimes in order to treat some critically ill patients, the hospital allows heroin to be used as a painkiller. In fact, this should be prohibited. Drug traffickers can obtain heroin through this channel, causing serious harm to society. Which of the following, if true, would most weaken the argument above? ['Some painkillers can have the same analgesic effect as heroin.', 'Heroin used for pain relief is insignificant compared to the amount used for illegal transactions.', 'Heroin can be fatal if it is used in excessive amounts.', 'Use of heroin during treatment does not make patients addicted.']