Ritonavir is a well-known inhibitor of most of these enzymes and is commonly used to increase the concentration of other drugs in the body by non-specifically blocking the enzyme's normal metabolic function. It was initially developed as a protease inhibitor, in particular to HIV, but is now commonly used as an activator of other drugs by inhibiting the CYP enzymes, amongst other proteins. The molecule Ritonavir is large and flexible and sticks to almost any protein; it is not a precision designed small molecule, but the body can metabolize it. The problem with Ritonavir, and as a result with the Paxlovid therapeutic, is that by inhibiting these enzymes it also blocks the metabolism of a number of other molecules and drugs , including commonly used anti-depressants and cholesterol medicines. The use of Ritonavir could send a normal medication or dose of prescribed medication into a toxic level. There are a variety of side effects of Ritonavir . As a result, Paxlovid is primarily intended for high risk groups in its FDA approval , which is about 2% of the population in the US. It was announced in June 2022 to be effective primarily only in this group.