Rhythms of daily consumption of psychoactive substances and chronotype effects

The present work studies the habits and diurnal rhythms of alcohol, nicotin e and caffeine (coffee, tea and cola) consumption, and also analyzes differ ences between chronotype groups (morning, evening and neither-types). A sam ple of 672 students (242 men/430 women) who answered a self-reported questi onnaire of daily substance consumption and by hourly intervals (waking time -12:00 h., 12:00-15:00 h., 15:00-18:00 h., and from 18:00-time to bed). All the substances showed a significant diurnal variation in consumption, alth ough the maximum for stimulating substances depended on the type and modali ty of ingestion. Generally, the level of consumption was higher in evening- type, lower for morning-type and intermediate for neither-type. The diurnal patterns for ingestion also differed between chronotypes, except for tea. Morning-types showed an advanced in the maximum consumption of alcohol, nic otine and cola (15:00-18:0 h.) when compared to the other groups. Chronotyp e is an individual difference which must be integrated in a multifactorial model explaining the consumption behaviour of psychoactive substances. Key words: alcohol, psychostimulant substances, diurnal rhythm, chronotype.