When you miss a step and fall, resulting in excruciating pain in your knee… you take a painkiller. When you accidentally cut your finger while making dinner… you take a painkiller. When you have an inexplicable headache… you take a painkiller. How do these pain killers seem to work in all of these areas of the body? How does the medication know where the pain is? Pharmacology, a branch of medicine that focuses on studying the uses, effects and mechanisms of action of drugs, helps in providing answers to such questions.
So, here goes… When you swallow a painkiller, it dissolves in the stomach or sometimes the small intestines before it is absorbed into the whole body. Pills are not smart enough to only travel to the place where their action is required. However, the secret to the function of painkillers depends on the mechanism with which pain is mediated in the human body.
When one is injured, cells release molecules called prostaglandins, and nerve endings are sensitive to these prostaglandins. Following prostaglandin release, nerves then transmit signals to the brain communicate the intensity and site of the pain. It would make sense then to reduce the synthesis of prostaglandins to stop transmission of the pain signals, right? This is exactly how pain relievers like aspirin work. They are distributed throughout the body, and reduce prostaglandin synthesis, reducing the transmission of pain signals.
Therefore, a painkiller does not know where the pain actually is, but it works by reducing prostaglandin synthesis in areas where there high levels of production of these chemical mediators of pain, resulting in relief.
However, since the drug travels throughout the whole body, it could potentially work where it is not supposed to, and this unfortunately results in side effects. Regarding pain reduction, prostaglandins are not only released in injured cells, but specific types of prostaglandins are constantly produced by the body for the maintenance of normal bodily functions. As shown in the figure below.
Reduction of the prostaglandins needed for normal bodily functions leads to various side effects. For example, the use of pain killers may result in the loss of prostaglandins needed for protection of the stomach, leading to stomach ulcers. Fortunately, prior to the use of drugs, clinical trials are typically conducted to investigate that any side effects are not detrimental to life.
The phenomenon of how drugs work is not only limited to painkillers. Although many drugs are distributed throughout the body, their main action is based on correcting the abnormalities that occur in the biology of various diseases. For example, many anti-cancer drugs work by targeting cells that grow at a fast rate. Though the medication will kill the fast-growing cancer cells, it will also result in the loss of healthy cells that grow fast, like hair follicles, leading to side effects like hair loss. Therefore, when taking any type of medication, one should keep in mind that the distribution of drugs in the body could result in undesired side effects, and overuse of over-the-counter medications should thus be avoided.
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