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Naproxen and aspirin are both widely available medications that are used to control mild to moderate pain. Individuals sometimes combine these medications in an effort to receive more pain relief. Mixing these medications on occasion may not be harmful, but there are distinct interactions between the two that can make high-dose or high-frequency combinations decidedly unsafe.
Both of these medications have distinct, albeit overlapping, ways that they affect the human body, which contributes to their safety level when combined. Naproxen and aspirin both inhibit the cyclooxygenase-2 (COX-1) enzyme involved in the inflammation reaction of the immune system. By doing so, they reduce pain and swelling. They also inhibit a type of COX enzyme in the stomach, COX-1, involved in protecting stomach tissue from stomach acid, however, leading to a risk of stomach damage when either is taken on its own.
Research has shown that taking naproxen with aspirin greatly increases the chance of damage to the stomach. This risk is greater than taking higher doses of either medication alone. Users of both medications simultaneously, at therapeutic dosages, were twice as likely to experience problems like stomach perforation, stomach bleeding, and ulcers. These drugs taken together can be considered unsafe, even at relatively low dosages.
Aspirin is sometimes taken for the protective effect it can have on the heart, based on its ability to prevent blood cells from clotting inside the bloodstream. Studies have shown that this effect, which is caused by aspirin's inhibition of COX-1, is prevented when naproxen and aspirin are taken within two hours of one another. People taking aspirin to prevent heart attacks may not receive this beneficial effect if both medications are taken in a short period of time.
The similarities of naproxen and aspirin in their mechanisms of action mean that they have similar side effects, as well. Potential side effects can increase in severity and frequency when they are taken at the same time. Less severe side effects that may result from this combination can include nausea, heartburn, and upset stomach.
Medical assistance should be sought immediately if more severe side effects appear after taking either or both of these drugs. Blood in the urine or stool, stomach pain, or a persistent fever are effects that can potentially result from these medications. They can be indicative of serious medical conditions, such as stomach bleeding. As determined by the studies mentioned above, these effects are more likely to occur if both drugs are taken together.