Objective The tobacco industry often relies on the assertion that smokers make ‘informed adult choices’. We tested this argument by exploring how young adults initiate smoking.

Methods Fifteen in-depth interviews with young adults who had started smoking since turning 18, the legal age of adulthood and tobacco purchase in New Zealand. We undertook a thematic analysis of the interview transcripts.

Results Although participants had a general awareness that smoking is harmful and knew some specific risks, they rarely saw these as personally relevant when they started smoking, and few had made a deliberate decision to smoke. Participants’ poor understanding of addiction meant most regarded smoking as a short-term phase they could stop at will. Initiation contexts discouraged the exercise of informed choice, as smoking onset often occurred when participants were influenced by alcohol or located in socially-pressured situations that fostered spur of the moment decisions.

Conclusions Young adults’ ability to exercise ‘informed choice’ at the time of smoking uptake is constrained by cognitive and contextual factors. We propose an updated informed choice framework that recognises these factors; we outline environmental changes that could make default adoption of smoking less common while promoting more ‘informed choices’.