Tylenol (the trademark name for acetaminophen or paracetamol) is a common drug used to control fever and pain. The metabolism of Tylenol involves liver enzymes, which are also required for the metabolism of alcohol. In layman’s terms, Tylenol metabolism requires two steps:
- Tylenol is broken down by a liver enzyme, cytochrome P450 CYP2E1 and CYP1A2, into a toxic free radical known as NAPQI
- The toxic free radical, NAPQI, reacts with an antioxidant, glutathione, and is detoxified
When a person drinks alcohol, Tylenol can become toxic. Alcohol affects this pathway in two ways:
- Firstly, chronic alcoholism causes an increase in the cytochrome P450 enzymes causing an increased rate of conversion of Tylenol into the toxic free radical, NAPQI.
- Secondly, when alcohol is consumed, your liver assigns the antioxidant, glutathione, to breakdown alcohol instead of the toxic free radical, NAPQI.
Therefore, with glutatione prioritized to breakdown alcohol, the toxic NAPQI accumulates and kills liver cells. That is why chronic alcoholics are not supposed to drink and you are never supposed to take tylenol when drinking alcohol.