Substance consumption behaviors can range from use to abuse, the latter including addictive behaviors. Relationships between emotionality, alexithymia and substance-consumption behaviors among young adults were investigated through an explanatory model wherein alexithymia fulfills a mediating function by acting as an emotion-adjustment process. 256 students (62.1% women) with a mean age of 20.7 yr. (SD = 1.6), enrolled at two universities in southern France took part in the study. They filled out a substance-use questionnaire, the Emotionnalite positive et negative a 31 (EPN-31) emotionality scale, and the 20-item Toronto Alexithymia Scale (TAS-20). Mediation analyses validated the hypothesis that emotional dimensions of alexithymia act as mediators between emotionality (negative emotionality and emotional arousal) and substance use. As a mediating factor, alexithymia may be regarded as a type of operational process that regulates emotions. These results could have important implications for clinical and therapeutic applications focusing on emotion-regulation strategies and substance use.