The use of both legal and illegal drugs has rarely been investigated among the Spanish military population involved in multinational military operations. The aim of the current study was to examine the consumption of drugs by Spanish military personnel in Bosnia-Herzegovina, and the variables associated with such substance use. A total of 605 military personnel participated in the cross-sectional study. The participants' mean age was 25.9 years (SD = 5.9), and 93.9% of the sample was male. The majority of the participants were enlisted personnel (83.5%). The most widely used drugs were tobacco (54.2%), and alcohol (39.9%). With respect to illegal drugs, the results showed that the drug with the highest prevalence of 'use at some point during a lifetime' was cannabis (36.2%), followed by cocaine (14.9%) and amphetamines (12.1%). The most important variable associated with a decrease in the consumption of illegal drugs was social support. Conversely, participants with friends who have used illegal drugs had an increased likelihood of drug consumption. Given that the use of drugs can adversely affect soldiers' performance, preventive measures should be applied in multinational military operations.