The most frequent underlying diseases justifying drug treatment are infections (52.7%) and pain (36%)
Residential indoor air quality guideline: nitrogen dioxide, accessed 02 July 2020
Smoking causes many already known background diseases that raise the risk of serious morbidity [illness] and mortality from corona chronic obstructive pulmonary disease, heart disease, and diabetes

Nguyen Department of Surgery, Danang Family Hospital, Danang, Viet Nam Phat Tuan Nguyen Tuberculosis Group, Oxford University Clinical Research Unit, Vietnam, Ho Chi Minh City, Viet Nam Van Thanh Nguyen Department of General Medicine, University of Medicine and Pharmacy at Ho Chi Minh City, Ho Chi Minh City, Viet Nam Van Thanh Nguyen International Islamic University Islamabad, Islamabad, Pakistan Robina Khan Niazi School of Chemical & Biomolecular Engineering, University of Sydney, Sydney, New South Wales, Australia Efaq Ali Noman Faculty of Applied Sciences, Taiz University, Taiz, Yemen Efaq Ali Noman Global Research Institute, Keio University, Tokyo, Japan Shuhei Nomura Department of Global Health Policy, University of Tokyo, Tokyo, Japan Shuhei Nomura Department of Statistics, Shahjalal University of Science and Technology, Sylhet, Bangladesh Syed Toukir Ahmed Noor School of Medicine, Xiamen University, Xiamen, China N

After three or four packs, most switchers report not noticing the difference