Pain signals that something is wrong in your body, whether it be an injury or illness. Regardless of where pain originates, the pain message is processed in the brain. Nerve endings at the site of the injury or illness transmit the pain messages to the brain. Pain medications do not fix the problem that is causing the pain, but they diminish the pain messages until the body has time to heal.
Opiates
The opiate family of pain medications includes drugs like morphine, codeine, hydrocodone, fentanyl and oxycodone. These drugs stimulate the mu receptors on nerve endings. Stimulation of the mu receptors lessens the ability of the body to feel pain. Since opiates work all along the central nervous system, they can decrease the cascading affect of the pain message as it travels along the nerves and spinal cord.
The mu receptors have many other functions other than the transmission of pain, which result in side effects such as repressed respiration, drowsiness and constipation. Opiates also cause feelings of euphoria, which makes them likely to be abused.
Tramadol
Tramadol weakly stimulates the mu receptor, but it also increases the amount of the neurotransmitters serotonin and norepinephrine in the central nervous system. These neurotransmitters suppress pain signals in the central nervous system.
NSAIDs
Prostaglandins are substances that have many jobs in the human body, from forming a barrier that protects the stomach from digestive acids to sending pain signals. Prostaglandins are also responsible for stimulating inflammation in the tissues and causing fever. NSAIDS, or non-steroidal anti-inflammatory drugs, block the synthesis of prostaglandins.
NSAIDS often cause stomach upset; the family of NSAIDS known as COX-2 selective inhibitors, like Celebrex and Mobic, do not affect prostaglandins in the stomach. The COX-2 selective inhibitors cause much less stomach upset, but in some patients stomach upset still occurs.
Acetaminophen
Acetaminophen, commonly known by the brand name Tylenol, also affects prostaglandin synthesis, but only in the central nervous system. New information shows that acetaminophen might block prostaglandin synthesis in an enzyme known as COX-3, which is only found in the central nervous system.
Antidepressants
Antidepressants relieve depression by increasing the levels of neurotransmitters like serotonin and norepinephrine in the central nervous system. Higher levels of these neurotransmitters decrease the transmission of the pain signals. Tricyclic antidepressants, selective serotonin reuptake inhibitors (SSRI) and serotonin-norepinephrine reuptake inhibitors (SNRI) are all used for pain management, but they are reserved for chronic pain conditions, such as fibromyalgia or diabetic neuropathy.
Anticonvulsants
Anticonvulsants reduce seizures by decreasing the excitability of the nervous system. They also decrease the transmission of pain signals. Like the antidepressants, anticonvulsants are used for chronic pain conditions.
References
- Basic and Clinical Pharmacology; Bertram Katzung; 2007
- U.S. Pharmacist on Chronic Pain Management
- U.S. Pharmacist on Chronic Lower Back Pain
