BACKGROUND: Pregnant smokers may be offered nicotine replacement therapy (NRT) alongside behavioral support to assist with a quit attempt. Yet trials of NRT have found adherence to be low among pregnant women, and this has made it difficult to determine the efficacy of NRT. The aim of this study is to understand the experience of pregnant women who use NRT but discontinue this early or do not use the medication as recommended. METHODS: Semi-structured telephone interviews were conducted with 14 pregnant smokers who had recently been prescribed NRT, but self-reported poor NRT adherence or discontinuing treatment prematurely. Data were transcribed and analyzed using inductive thematic analysis RESULTS: There were four main themes identified; expectations of NRT, experience of using NRT, safety concerns and experience of using e-cigarettes. Some women intentionally used NRT to substitute a proportion of their cigarette intake and smoked alongside. Most women smoked while using NRT. Women who underutilized NRT did so as they experienced side effects, or were concerned that using NRT instead of smoking could actually increase their nicotine exposure and potential for increased nicotine dependence or fetal harm. Most women spoke about the use of e-cigarettes as a smoking cessation method but only a few had actually experienced using them during pregnancy. CONCLUSION: Many women underused NRT but simultaneously smoked. Challenging negative perceptions about NRT and educating women further about the risks of smoking may encourage them to use NRT products as recommended. IMPLICATIONS: These findings add to the research surrounding the efficacy of NRT during pregnancy by providing insight into how pregnant women use NRT during a quit attempt and how this may influence adherence. It may assist health professionals to support pregnant smokers by increasing their understanding about the differing ways in which women use NRT and help them address concerns women may have about the safety of NRT.