Purpose: Sexual minority women and gender diverse individuals assigned female at birth (SMWGD) are at elevated risk for alcohol and cannabis use disorders. It has been posited that characteristics of SMWGD's substance use companions (i.e., sexual orientation, gender identity) may influence their own use, but few studies have tested this. The current study aimed to examine whether quantity and consequences of substance use varied based on sexual orientations and gender identities (SOGI) of SMWGD's substance use companions.

Methods: We utilized a 30-day ecological momentary assessment study of substance use among a sample of 429 SMWGD. We examined event-level associations between characteristics of substance use companions and quantity and consequences of substance use.

Results: When SMWGD used alcohol/cannabis with most SOGI groups, they engaged in heavier drinking and cannabis use. Drinking with heterosexual men and SMW was associated with more drinking consequences. Drinking in settings with more SOGI groups and with both LGBTQ+ and heterosexual individuals was associated with heavier drinking and more consequences. Many contextual aspects of cannabis use settings predicted an increased likelihood of alcohol and cannabis co-use, while few contextual aspects of drinking settings were associated with co-use.

Conclusion: Results suggest that SMWGD engage in heavier substance use when individuals from a range of SOGI groups are present, highlighting that heavy alcohol and cannabis use is not limited to use with SMW and nonbinary individuals. Drinking in setting with more SOGI groups present (e.g., parties and bars) appears to be associated with particularly heavy drinking and consequences.