The CYP1A2 isoenzyme, also known as CYPIA2, is a member of the cytochrome P450 family of enzymes that are responsible for the metabolism of various drugs and endogenous compounds in the liver. Methadone is not a substrate for the CYP1A2 isoenzyme. Instead, it is primarily metabolized by other cytochrome P450 enzymes, particularly CYP2B6 and CYP3A4.

**_ Caffeine is a well-known substrate for the CYP1A2 isoenzyme. The enzyme metabolizes caffeine into paraxanthine, which is further broken down into other metabolites. Paracetamol is metabolized by several cytochrome P450 enzymes, including CYP1A2. While it is not the primary pathway, CYP1A2 does play a role in its metabolism. Tacrine, a drug used in the treatment of Alzheimer’s disease, is also a substrate for the CYP1A2 isoenzyme. The enzyme helps in the breakdown and elimination of Tacrine from the body. Among the given options, Methadone is not a substrate for the CYP1A2 isoenzyme. The other options—Caffeine, Paracetamol, and Tacrine—are all metabolized to some extent by CYP1A2. Understanding the specific enzymes involved in drug metabolism is crucial for predicting drug interactions and personalizing medical treatments.