Without the ability to feel pain, life is more dangerous. To avoid injury, pain tells us to use a hammer more gently, wait for the soup to cool or put on gloves in a snowball fight. Those with rare inherited disorders that leave them without the ability to feel pain are unable to protect themselves from environmental threats, leading to broken bones, damaged skin, infections and ultimately a shorter life span.
In these contexts, pain is much more than a sensation: It is a protective call to action. But pain that is too intense or long-lasting can be debilitating. So how does modern medicine soften the call?
As a neurobiologist and an anesthesiologist who study pain, this is a question we and other researchers have tried to answer. Science’s understanding of how the body senses tissue damage and perceives it as pain has progressed tremendously over the past several years. It has become clear that there are multiple pathways that signal tissue damage to the brain and sound the pain alarm bell.
Interestingly, while the brain uses different pain signaling pathways depending on the type of damage, there is also redundancy to these pathways. Even more intriguing, these neural pathways morph and amplify signals in the case of chronic pain and pain caused by conditions affecting nerves themselves, even though the protective function of pain is no longer needed.
Painkillers work by tackling different parts of these pathways. Not every painkiller works for every type of pain, however. Because of the multitude and redundancy of pain pathways, a perfect painkiller is elusive. But in the meantime, understanding how existing painkillers work helps medical providers and patients use them for the best results.
Anti-inflammatory painkillers
A bruise, sprain or broken bone from an injury all lead to tissue inflammation, an immune response that can lead to swelling and redness as the body tries to heal. Specialized nerve cells in the area of the injury called nociceptors sense the inflammatory chemicals the body produces and send pain signals to the brain.
Common over-the-counter anti-inflammatory painkillers work by decreasing inflammation in the injured area. These are particularly useful for musculoskeletal injuries or other pain problems caused by inflammation such as arthritis.
Nonsteroidal anti-inflammatories like ibuprofen (Advil, Motrin), naproxen (Aleve) and aspirin do this by blocking an enzyme called COX that plays a key role in a biochemical cascade that produces inflammatory chemicals. Blocking the cascade decreases the amount of inflammatory chemicals, and thereby reduces the pain signals sent to the brain. While acetaminophen (Tylenol), also known as paracetamol, doesn’t reduce inflammation as NSAIDs do, it also inhibits COX enzymes and has similar pain-reducing effects.
Prescription anti-inflammatory painkillers include other COX inhibitors, corticosteroids and, more recently, drugs that target and inactivate the…