This study aimed to document changes in puffing topography and, the effects of device type and nicotine concentration on puffing topography, subjective effects and smoking behaviour over two weeks of e-cigarette (EC) use. [...] Two weeks post-baseline, puff duration and IPI significantly increased whilst puff number decreased. Cigalikes were associated with greater puff number and shorter IPI compared to Tanks; there was no difference between Tank18 and Tank6. CPD, CO and cigarette dependence reduced significantly from baseline to week1 but did not differ between conditions.