PART 1: What Tylenol Actually Does Inside Your Body Ever popped a Tylenol and wondered what's happening inside you? Let's trace this common pain reliever through your anatomy. THE JOURNEY: Tylenol (acetaminophen/paracetamol) starts in your oral cavity, travels down your esophagus to your stomach where it begins dissolving in stomach acid. But here's the key - it's NOT absorbed in the stomach. The real absorption happens in your duodenum (first part of small intestine). From tablet to pain relief