Actually, the article is not 100% clear - they first write about polycyclic aromatic hydrocarbons (PAHs) that are contained in cigarette smoke and are likely to be the "active ingredient" which decreases the coronavirus' ability to enter cells, but later they write that the scientists used "cigarette smoke extract" (CSE) for their study, and it remains unclear what this CSE contained exactly. But apparently it is the PAHs, because these can bind to and activate aryl hydrocarbon receptors (AHRs), and two drugs which do the same have the same effect...