Women's initiation into injection drug use often establishes a pattern of risk following first injection. This study explored sources of gendered power dynamics in injection initiation experiences for people who inject drugs. A qualitative subsample from two prospective community-recruited cohorts of people who inject drugs in San Diego and Tijuana provided data on the contexts surrounding injection initiation processes. Intimate partnerships were identified in initiation; sub-themes were identified drawing on three concepts within the theory of gender and power. With reference to sexual division of labour, men were often responsible for access to resources in partnerships across both contexts, although there were limited accounts of women obtaining those resources. Extending the structure of power, women in San Diego reported that initiation events involving an intimate partner occurred from a position of vulnerability but expressed greater agency when providing initiation assistance. With regard to structure of cathexis, social norms proscribing injection initiation among women exist, particularly in Tijuana. Gendered power dynamics are a multifaceted component of injection initiation events, especially for women in intimate partnerships. These results stress the need for nuance in understanding the intersection of risk, gender and harm reduction within injection initiation events across socio-cultural contexts.