Lariam is an antimalarial drug that has a safety profile characterised by a predominance of neuropsychiatric adverse reactions. It is still prescribed within the British armed forces. A purposive survey (n = 28) of serving and ex-serving British military personnel with experience of operations where Lariam was used revealed that 82% experienced side effects and 85.71% considered the drug unsuitable for use during military operations. An additional online survey (n = 50) provided supporting results. Using system theory analysis, Peta Bathie argues that Lariam use degrades decision-making, damages unit morale and erodes cohesiveness. Because it undermines fighting power, the consumption of such antimalarials appears inconsistent with current UK military doctrine.