How do painkillers work?

When tissue is injured, cells release prostaglandins that make nerve endings more sensitive and cause inflammation. Non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and aspirin block the COX enzymes that produce prostaglandins, reducing both pain and swelling. Paracetamol, also called acetaminophen, relieves pain and fever, but exactly how it works is still not fully understood; it seems to act mainly in the brain. Opioids such as morphine bind to opioid receptors in the nervous system, blocking pain signals, but carry risks of dependence. Local anaesthetics work differently, stopping nerves from sending signals at all.