The use of alcohol, drugs, inhalants, and smoking tobacco may lead to mood disorders such as depression. However, knowledge on the independent contributions of the use of these substances to the risk of depression is lacking.
The study cohort consisted of 24,564 men included in the Swedish national military conscription register who were conscripted in 1969-1970 and followed until 2017. Cox proportional hazard ratios were used to estimate the risk of depression according to alcohol, drug, inhalant, and cigarette consumption, and adjusted for body mass index, verbal comprehension test scores, handgrip strength, and the other main exposures investigated.
During an average follow-up period of 44 years, 4500 men were diagnosed with or treated for depression at a mean age of 54 years. A dose-dependent association was found in men who smoked cigarettes, with the highest risk for smoking >20 cigarettes per day, at time of conscription (aHR 1.86, 95 % CI 1.61-2.16, p < 0.001). Independent associations with an increased risk of depression were found for the use of drugs at least once (aHR 1.21, 95 % CI 1.10-1.32, p 50 times (aHR 1.48, 95 % CI 1.23-1.77, p < 0.001) and the use of inhalants (aHR 1.16, 95 % CI 1.05-1.29). Excessive alcohol intake was not associated with the risk of depression.
The results suggest that people who reported to have used cigarettes, alcohol, or drugs at 18 years of age have a moderately increased risk of depression later in life.

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