The study is randomised cross-over trial designed to compare: 1) Cognitive performances levels for four different e-Cigarette strength. Participants will be requested to abstain from smoking and alcohol from 20:00 on the night before each study day and from food and caffeine for at least 1 h before the session. On arrival at the study centre, carbon monoxide (CO) will be measured in participants' expired breath. If CO will be >15 parts per million (ppm), the assigned study treatment will be allocated; however, if CO was >15 ppm or they will report smoking in the previous 12 h, participants will be rescheduled wherever possible to a subsequent session.