Aspirin can damage the lining of the stomach and duodenum, thereby causing abdominal pain, bleeding, and/or ulcers. As a result, 1 in 5 persons who take aspirin in a dose of 2.5 grams per day or more develops ulcers and about 1 in 6 will lose enough blood from gastrointestinal bleeding to develop anemia. In an attempt to reduce the potential for these complications, some aspirin-containing tablets have been coated with a special coating that prevents the tablet from dissolving until it is past the stomach and duodenum. These “enteric-coated” aspirin products may reduce the frequency of abdominal pain, but not the bleeding or ulcers. Moreover, the onset of pain relief is delayed with enteric-coated aspirin because it takes more time for the tablets to dissolve.

Other attempts to prevent complications have included aspirin-containing products that release the aspirin slowly over time (for example, Zorprin, Measurin, Verin). Like enteric-coated products, these products are not ideal when prompt relief of pain is needed. They also do not prevent ulcers or bleeding. Buffered (for example, Bufferin) and effervescent (such as Alka-Seltzer) aspirin products are absorbed more quickly from the stomach and intestine than aspirin, but they do not act more rapidly than regular aspirin and do not reduce the risk of bleeding or ulcers. Furthermore, effervescent aspirin products contain large amounts of sodium (salt) and should be avoided in persons with high blood pressure, heart failure, or certain kidney diseases.

Side effects of aspirin

Aspirin prevents platelets from their natural ability to stick together and form blood clots. On the one hand, this effect can be used beneficially, such as to prevent the blood clots that cause heart attacks or strokes. On the other hand, by preventing blood clots, aspirin can have the detrimental effect of promoting bleeding. Therefore, aspirin should not be used by people who have diseases that cause bleeding (such as hemophilia and severe liver disease) or diseases in which bleeding may occur as a complication (such as stomach ulcers). Moreover, since the effect of aspirin on platelets lasts for many days, people should not take aspirin for at least seven days before surgical or dental procedures because of the increased risk of bleeding after the procedures.

In patients at risk for bleeding, acetaminophen can be an excellent alternative to aspirin since acetaminophen does not have an effect on platelets, blood clots, or bleeding.

Like aspirin, other NSAIDs affect platelets, but the duration of the effect is less than with aspirin. Two aspirin-related, salicylate-containing products (salsalate and choline magnesium trisalicylate) have no effect on the platelets, but they are available only by prescription.

Serious side effects of aspirin occur infrequently. However, they may occur and generally tend to be more frequent with higher doses. Therefore, it is advisable to use the lowest effective dose to minimize side effects.

The most common side effects of aspirin involve the gastrointestinal system. Aspirin can cause ulcers of the stomach and duodenum (first part of the small intestine), abdominal pain, nausea, gastritis (inflammation of the stomach), and even serious gastrointestinal bleeding from ulcers. Sometimes, ulcers of the stomach and bleeding occur without any abdominal pain, and the only signs of bleeding may be bloody or dark stools or weakness.

Although many people claim to be “allergic” to aspirin, most describe their “allergy” as abdominal pain or heartburn. These common side effects are not allergies, but rather reflect the irritating effects of aspirin on the lining of the stomach. True allergy to aspirin is a rare and serious condition in which a patient can develop swelling of tissues, spasm of the airways (bronchospasm) that causes difficulty breathing, and even anaphylaxis, a life-threatening condition. Clearly, patients with a history of allergy to aspirin should not take aspirin. Since aspirin is related chemically to the other NSAIDs, patients who are allergic to the other NSAIDs, such as ibuprofen (Motrin) and naproxen (Aleve), should also not take aspirin.

Pregnancy/breastfeeding and aspirin

Regular aspirin consumption during pregnancy has been associated with side effects in the pregnant mother, including bleeding and complications during labor. It is unclear if aspirin taken in the first two trimesters poses a risk to the fetus. However, when taken during the third trimester, aspirin may increase the risk of bleeding in the newborn. Nevertheless, for certain mothers with diseases that are associated with a high risk for blood clotting during pregnancy and miscarriage, aspirin is actually recommended in low doses for prevention. Although very little aspirin is secreted into breast milk, most authorities recommend that nursing mothers avoid using aspirin. A woman should consult with her health care practitioner before taking any medications while pregnant or breastfeeding.

Viral infections in children and aspirin

Because aspirin causes Reye’s syndrome (a potentially fatal liver disease that occurs almost exclusively in persons under the age of 15 years), aspirin should not be given to children when a viral infection is suspected.

Drug interactions and aspirin

Aspirin may interact with other medications and cause undesirable side effects. For example, high doses of aspirin can increase the activity of valproic acid (Depakene; Depakote), an effect which can cause drowsiness or behavioral changes.

High doses of aspirin also can enhance the effect of some blood sugar-lowering medications used to treat diabetes, including glyburide (Diabeta), glipizide (Glucotrol), and tolbutamide (Orinase), which can possibly lead to hypoglycemia (low blood sugar). Blood sugar levels may need to be more closely monitored in this setting.

Aspirin, when taken together with an anti-coagulant such as warfarin (Coumadin) or enoxaparin (Lovenox), can greatly impair the body’s ability to form blood clots, resulting in excessive bleeding spontaneously, from ulcers, or related to a procedure. Therefore, patients on such combinations must be closely monitored by a doctor.

Low dose aspirin can raise levels of uric acid in the blood and may need to be avoided in patients with increased uric acid levels or gout.

Certain NSAIDs, particularly ibuprofen (Motrin, Advil), if taken just before aspirin or in multiples doses each day, can reduce the anti-platelet effects of aspirin treatment and theoretically render aspirin less effective in preventing heart attacks and ischemic strokes.

Salicylates other than aspirin

Choline salicylate (Arthropan) is available as a liquid. It is absorbed more quickly, but its onset of action is no different than that of aspirin. Some people find choline salicylate fishy tasting. Fortunately, it can be mixed with juice or soda prior to ingestion. It is less effective at reducing fevers in children than either aspirin or acetaminophen.

Magnesium salicylate (Arthriten; Backache) is as effective as aspirin at reducing pain. Patients with chronic kidney disease should avoid magnesium salicylate, since the magnesium may accumulate in the body.

Sodium salicylate (Scot-Tussin Original) and aspirin are equally effective in the long-term treatment of rheumatoid arthritis, but sodium salicylate is less effective at reducing pain or fever.