How do analgesics work on pain?
Answered by Craig C. Freudenrich and Discovery Fit & Health
  • Craig C. Freudenrich

    Craig C. Freudenrich

  • Discovery Fit & Health

    Discovery Fit & Health

  1. When you're injured or have a headache, you reach for the bottle of pain relievers. All that matters at that point is that the pills or capsules work -- and quickly. To understand how analgesics relieve pain, it helps to first understand how your brain perceives pain. Pain perception, or nociception, is the process by which a painful stimulus is relayed from the site where you're injured to the central nervous system (brain, spinal cord). There are several steps in this process:

    1. Injury -- Mechanical  injuries, such as pressure, punctures and cuts or chemical (burn) stimuli injure tissues. The injured tissues release chemicals (potassium, prostaglandins, histamines, bradykinin and substance P).

    2. Reception -- A specialized nerve cell called a nociceptor senses the stimulus and the chemicals released from injured tissues.

    3. Transmission -- The nociceptor sends signals to the brain through several neurons within the central nervous system. The signals travel up the spinal cord to the brain through a "neural freeway" called the spinothalamic tract.

    4. Pain center reception -- Within the brain, a relay station called the thalamus distributes the signals to various parts of the brain; there is no single pain center. Areas like the somatosensory cortex process the information and you feel pain.

    5. Pain suppression or relief (analgesia) -- The somatosensory cortex, thalamus and hypothalamus send impulses through descending pathways that inhibit the spinothalamic tract within the medulla. Basically, the descending impulses inhibit the ascending pain impulses and provide some relief. Some of these signals release natural pain-relieving chemicals called endorphins, dynorphins and enkephalins. These chemicals inhibit the transmission of nerve impulses from one neuron to another in the pain pathways within the central nervous system.

    Analgesics relieve pain in a number of ways. Non-opioid analgesics, such as aspirin, ibuprofen, acetaminophen, naproxen and similar nonsteroidal anti-inflammatory drugs, act at the site of injury. They prevent inflammation and block key enzymes and the release of chemicals that stimulate nociceptors. Opioid analgesics, such as morphine, fentanyl and oxycodone act like the natural pain-relieving chemicals your body releases. Although they are not analgesics, antidepressant and anti-epileptic drugs inhibit the transmission of nerve impulses within the brain and thereby can help relieve pain; these substances are called co-analgesics.


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  2. Even the scientists and doctors who make and prescribe analgesics don't know exactly how they work to relieve pain, but they know that the medications can be very effective. There are two main types of analgesics: those that are narcotic and derived from opium, and those that are non-narcotic. (Narcotic painkillers can make people feel drowsy, so they should be used with caution. They also can be addictive, and therefore can potentially be abused.) In addition, some analgesics are combinations of the two. Analgesics act on the brain to deaden pain, and may also have anti-inflammatory effects.

    Some analgesics are used in cough medicines; some are used to treat arthritis. There are a host of analgesic brands available both over the counter and through a doctor's prescription. Aspirin and ibuprofen are among the most-used nonprescription drugs (Naprosyn and Aleve would be two other such examples). They are among a group of pain medications called NSAIDs (Non-steroidal anti-inflammatory drugs). While aspirin, ibuprofen (such as Advil or Motrin), Naprosyn and Aleve can be bought over-the-counter, some other NSAIDs require a doctor's presecription. The latter include drug brands such as Celebrex, Ansaid and Seractil. NSAIDs not only relieve pain but can also reduce swelling. (Note that aspirin should not be given to children, and those with heart trouble, high blood pressure, kidney disease or stomach of digestive tract bleeding should consult a doctor before taking over-the-counter NSAIDs [source: NIH].)

    Acetaminophen can also be had over-the-counter as a means to relieve pain. It's a non-aspirin analgesic that can knock back a fever, ease headache symptoms and handle other assorted pains. It's considered safer for children than aspirin; it's easier on the stomach than aspirin; and it's the recommended first choice of action for arthritis relief, thanks to its lesser side effects relative to other analgesics. (It should not be taken in doses of more than 4 grams per day as it can damage the liver [source: NIH].

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