Introduction: Gender dynamics and interpersonal relations within intimate partnerships are known to determine health behaviors, including substance use, within couples. In addition, influence from intimate partners may occur in the context of wider social ecological determinants of health behavior. The aim of this study was to document the role of intimate partners in influencing injecting drug use among women in Kenya, where injecting drug use is on the rise. Methods: We performed secondary data analysis of an existing dataset from a 2015 qualitative study involving 45 women who inject drugs and 5 key stakeholders in coastal Kenya. Primary data had been collected via a combination of in-depth interviews and focus group discussions exploring sexual, reproductive, drug use, and other social contexts of women who inject drugs. The process by which intimate partners influenced women's initiation of drug use, transition to injecting practices, and maintenance of injecting drug use were identified using thematic analysis. Results: Boyfriends and intimate either facilitated or restrained women's drug-injecting. On the one hand, young women's entry into drug use was prompted by relationship problems or a need to acquiesce with their drug-using boyfriends. Once women started injecting, intimate partners facilitated ongoing drug-injecting by financing the acquisition of drugs, peddling drugs to their women, or sharing their drugs with their women. The social capital that peddlers held insulated women from police arrests, and encouraged women to seek and sustain intimate relations with well-connected peddlers. Men's influences over women were driven by an underlying patriarchal drug acquisition and economic power. On the other hand, boyfriends and intimate partners who were non-injectors or non-drug users sought to moderate women's injecting drug use by encouraging them to inject less, to smoke or snort instead of injecting, or to enroll into rehabilitation. These moderating influences were most prominent when couples were pregnant. Despite men being a source of practical and emotional support, women were frequently unable limit or alter their injecting drug use, due to its addictive nature. Men's disagreement with women's ongoing injecting strained relationships, and occasionally led to separation. Conclusions: Some boyfriends facilitated women's injecting drug use, while others moderated it, supporting assertions that intimate relationships can both be a site of injecting risks or protection. At the micro-level, these findings highlight an opportunity for couplebased interventions, leveraging on non-drug injecting males as a resource to support women adopt safer injecting practices. At a macro level, incorporating livelihood interventions into harm reduction programs is required in order to mitigate economic-based influence of male intimate partners on women's injecting drug use. At both levels, gender transformative approaches are essential. To gain a comprehensive understanding of women's injecting drug use, future stu...