Background:
Marijuana use is associated with sexual behaviors linked to increased STD risk. Previous research insufficiently addresses mood and relationship variables that indirectly affect condom use by direct effects on the likelihood of marijuana-associated coitus.

Objective:
To model the effects of marijuana-associated coitus as a mediator of event-level mood, sexual interest and relationship variables on condom use among adolescent women.


Method:
267 adolescent women provided diaries recording daily partner interactions, marijuana use (not associated with sex), mood, sexual activity, marijuana-associated coitus and condom use. Direct effects on marijuana-associated coitus (no/yes) included three measures of usual behavior: recent sexual activity (past seven days: no/yes), recent marijuana use (past seven days, not associated with sex: no/yes) and recent marijuana-associated coitus (past seven days: no/yes). Other predictors included vaginal bleeding (no/yes), partner support (4-items, α=0.93), partner time (1 item), positive mood (3-items, α=0.84), negative mood (3-items; α=0.81) and sexual interest (1 item). Measures postulated to have direct effects on event-level condom use were partner time, positive/negative mood, sexual interest, recent sexual activity, marijuana-associated coitus and usual condom use (past seven days: no/yes). Adolescents without marijuana use were excluded; structural equation modeling (AMOS, 5.0) was used.

Result:
Approximately 17.5% (806/4610) of all coital events were associated with marijuana. Marijuana-associated coitus was associated with decreased likelihood of condom use (Β=-0.038). Recent sexual activity (Β=-0.215), recent marijuana use (Β=0.746), recent marijuana-associated coitus (Β=0.349), vaginal bleeding (Β=-0.072), negative mood (Β=0.131) predicted marijuana-associated coitus, but were not directly linked to condom use. Usual condom use (Β=0.823), partner support (Β=0.012), partner time (Β=-0.011), sexual interest (Β=-0.012), recent sex (Β=-0.018) and marijuana-associated coitus (Β=-0.038) directly predicted condom use (all standardized; p<.05).

Conclusion:
Negative mood is indirectly linked to decreased condom use via marijuana-associated coitus.

Implications:
Both mood and substance use may be an appropriate focus for clinical STD prevention efforts.