They are all part of a group called cyclooxygenase inhibitors. These stop an enzyme called COX friom working, which inhibits production of pain transmitters. This can either be done systemically (such as with aspirin or paracetomol) or locally (ibuprofen gel). COX is triggered at the site of the pain as part of your bodies signalling system, so this is where the drug works. And anywhre else it finds cox too.Yes it travels to the site of pain, but if you take the pill form of neurofen then it travels everywhere else too. One of the downsides of this is that one of the COX enzymes is involved in suppressing leukotrienes, one of the key triggers for asthma. This can mean that an asthmatic taking aspirin, paracetomol or ibuprofen can get very severe attacks.