Because of the numerous health benefits it has been linked with, aspirin is often hailed as the "wonder drug."
Earlier this month, it was announced that researchers from the UK would be embarking on the biggest clinical trial of aspirin to date - the Add-Aspirin phase 3 trial - investigating whether the drug is effective for preventing cancer recurrence through a study of around 11,000 people.
The announcement has caused much excitement in the medical world, with many health experts claiming the trial could be "game-changing" if the drug is found effective, offering a non-expensive strategy to improve survival for cancer patients.
Cancer is just one in a long line of illnesses that aspirin may combat. But in the midst of potential health benefits comes a number of risks, a fact some health professionals believe is often overlooked.
"Because it's been around a long time people think 'it must be safe and it can't do me any harm,'" Prof. Peter Weissberg, medical director of the British Heart Foundation in the UK, told The Independent. "They are taking it 'just in case,' but it's much more dangerous than some other drugs which people get concerned about, like statins."
In this Spotlight, we take a closer look at the potential health benefits of aspirin, as well as the risks associated with the drug.
Aspirin: one of the most commonly used drugs worldwide
Aspirin is a drug that was developed by German research chemist Felix Hoffman, of pharmaceutical company Bayer, in 1897.
Hoffman created aspirin by developing a process to synthesize acetylsalicylic acid (ASA) - a synthetic derivative of a compound called salicin, which is found naturally in plants such as the willow tree.
Early clinical trials of aspirin found it was an effective treatment for pain, fever and inflammation. It is believed the drug produces these effects by inhibiting the production of pain-producing chemicals called prostaglandins. As such, aspirin is commonly used to help ease headache, muscle pain, toothaches and common colds, as well as swelling in arthritis.
More recently, however, researchers have discovered aspirin may also be an effective blood thinner, preventing the formation of blood clots in the arteries by blocking the production of a prostaglandin called thromboxane, which plays a key role in blood clotting.
The possible risks of aspirin use
However, as with any drug, there is a risk for side effects with regular aspirin use.
One of the most severe side effects of regular aspirin use is gastrointestinal bleeding, which can raise the risk of developing a stomach ulcer. If one already has a stomach ulcer, taking aspirin could cause further bleeding and be potentially life-threatening.
Aspirin may also interact with other drugs and increase risk of internal bleeding, particularly drugs with anti-clotting properties, such as warfarin, apixaban and dabigatran. Taking aspirin with some dietary supplements, such as evening primrose oil and fish oil, may also raise internal bleeding risk.
Studies have associated aspirin use with increased risk of age-related macular degeneration.
Some individuals are allergic to aspirin, with people who have asthma most at risk. An allergic reaction to the drug may cause swelling of the lips, mouth or throat, breathing problems and a skin rash.
Other side effects of aspirin include headache, nausea and vomiting, tinnitus and bruising.
Some studies have linked aspirin use with increased risk for other health conditions. In 2013, for example, a study published in JAMA Internal Medicine suggested long-term use of the drug may increase the risk of age-related macular degeneration - the primary cause of blindness among older adults.
Previous research has also linked aspirin use to greater risk for Reye's syndrome - a rare disorder characterized by swelling in the brain and liver, most common among children and teenagers.
Despite these potential risks, however, aspirin has become one of the most widely used over-the-counter drugs around the globe; more than 100 million standard aspirin tablets are produced every year.
But people are not just using the drug to relieve the odd headache or cold. It seems aspirin is growing in popularity as more people are taking the drug regularly with the aim of preventing numerous health conditions for which studies have suggested it is effective against.
Aspirin and heart health
As mentioned previously, one of the many benefits of aspirin is believed to be its ability to prevent the formation of blood clots.
Last year, Medical News Today reported on a study by researchers from Australia that found individuals with venous thromboembolism (VTE) - a condition comprised of deep vein thrombosis (blood clots in the legs) and pulmonary embolism (in which a blood clot breaks off and travels to the lungs) - saw a 42% reduction in blood clot recurrence with a 100-mg dose of aspirin daily.
This and numerous other studies hailing the anticoagulant properties of aspirin have led to recommendations that people at high risk for heart attack or stroke may benefit from daily aspirin therapy.
The American Heart Association (AHA), for example, recommend daily low-dose aspirin - under the instruction of a health care provider - for heart attack survivors and others at high risk of heart attack.
And last month, MNT reported on new guidelines issued by the US Preventive Services Task Force (USPSTF) that recommend daily low-dose aspirin for heart attack and stroke prevention for individuals aged 50-59 who are at high risk for cardiovascular disease.
The debate over whether aspirin should be administered to prevent first heart attack or stroke, however, continues. Last year, the US Food and Drug Administration (FDA) concluded that, while daily aspirin use can help prevent heart attack and stroke in high-risk individuals, there is insufficient evidence to suggest it is beneficial for primary prevention.
But despite the FDA's conclusion, a study reported by MNT earlier this year revealed that 1 in 10 patients in the US are inappropriately receiving daily low-dose aspirin to prevent a first heart attack or stroke.
First study author Dr. Ravi S. Hira, of the Baylor College of Medicine in Houston, TX, said the findings are a concern because the risks of daily aspirin use may outweigh the benefits for healthy individuals.
"Major coronary events are reduced 18% by aspirin, but at the cost of an increase of 54% of major extracranial bleeding," he explained. "Each two major coronary events have shown to be prevented by prophylactic aspirin at the cost of one major extracranial bleed. Yet, primary prevention with aspirin is widely applied."
What is more, some studies have associated regular aspirin use with increased risk of hemorrhagic stroke - a type of stroke caused by a blood leakage in the brain.
Aspirin and cancer
It is no wonder aspirin is about to enter the largest clinical trial to assess its efficacy against cancer; there is an overwhelming amount of evidence claiming the drug has anti-cancer properties.
Last year, MNT reported on a study published in the Journal of the National Cancer Institute suggesting daily aspirin may reduce the risk of ovarian cancer by 20%, while a more recent study linked long-term use of low-dose aspirin to reduced risk of colorectal cancer, or bowel cancer.
What is more, a study recently presented at the 2015 European Cancer Congress in Vienna, Austria, suggested aspirin could double survival for patients with gastrointestinal cancers.
The mentioned research is just a snippet of the studies that have associated aspirin use with lower cancer risk, and such studies have caused much excitement in the medical world, spurring the initiation of the aforementioned Add-Aspirin phase 3 trial.
"There's been some interesting research suggesting that aspirin could delay or stop early-stage cancers coming back but there's been no randomized trial to give clear proof," says Prof. Ruth Langley, of Cancer Research UK, who is heading the new trial. "The trial aims to answer this question once and for all." She adds:
"If we find that aspirin does stop these cancers returning, it could change future treatment - providing a cheap and simple way to help stop cancer coming back and helping more people survive."
While there is no doubt a positive result from this trial would be good news, some researchers have concerns about the use of daily aspirin for cancer prevention.
Contrary to previous research, a study published in JAMA earlier this year suggested regular aspirin use may actually increase the risk of bowel cancer for some people, with the effect of aspirin dependent on the presence of certain genetic variants.
The study authors say their findings indicate the importance of identifying which people are most likely to benefit from reduced bowel cancer risk with regular aspirin use. "Validation of these findings in additional populations may facilitate targeted colorectal cancer prevention strategies," they noted.
Aspirin and pregnancy
In recent years, researchers have suggested there may be a link between daily aspirin use and increased chance of conception.
MNT first reported on the association last year, when a study published in The Lancet found women with a history of miscarriage or stillbirth were more likely to have a successful pregnancy if they took 81 mg of aspirin daily with folic acid, compared with women who took a placebo.
Studies suggest regular aspirin use increases the chances of conception and a successful pregnancy.
A study presented at the American Society of Reproductive Medicine Annual Meeting in Baltimore, MD, last week supported such findings; in an analysis of more than 1,200 women with a history of miscarriage, those who took 81 mg of aspirin daily were 17% more likely to become pregnant and 20% more likely to have a successful birth than those who did not take the drug.
While it is unclear exactly how aspirin may boost the chances of pregnancy, the researchers speculate that the drug reduces systemic inflammation, making the womb a safer environment for the embryo to grow.
In addition, it is believed aspirin increases the flow of blood to the pelvis and thickens the womb lining, which can make it easier for the embryo to implant.
Many health care professionals are already recommending regular aspirin use to boost fertility.
"Aspirin is the drug of the millennium," says Dr. Richard Paulson, professor of obstetrics and gynecology at the University of Southern California Keck School of Medicine. "There is no harm in women wanting to get pregnant taking aspirin. Many people use it routinely, including in our clinics. We have been doing this for many years."
Other health experts, however, believe the risks of regular aspirin - such as internal bleeding - may outweigh the potential benefits of increased fertility for women.
"I don't think women trying to get pregnant should take an aspirin every day. The evidence does not support the need," Edgar Mocanu, treasurer of the International Federation of Fertility Societies (IFFS), told The Telegraph earlier this month.
Talk to a doctor before taking aspirin daily
Based on the evidence to date, there are likely some benefits with regular aspirin use, and some health professionals believe there is no doubt people should take the drug daily.
"This is clear-cut. Aspirin is cheap and effective,'' Peter Elwood, professor of epidemiology at the UK's University of Wales, told The Telegraph. "Taking aspirin every day will increase your chance of survival against serious diseases.''
However, most are in agreement that one should consult with a physician before engaging in daily aspirin therapy.
Last year, Dr. Phil Hammond, a general practitioner in the UK, told The Telegraph:
"Note, all drugs that have effects also tend to have side effects. Some can't be predicted, but some people are at higher risk of side effects from aspirin and probably do need to share the decision to take it with a doctor or pharmacist - even if you are just taking it for pain relief."
Some people at higher risk for side effects from aspirin include pregnant women and people who have high blood pressure, asthma, liver or kidney problems, a blood disorder or allergies to any other medications.
The drug should also not be given to children under the age of 16 due to the increased risk of Reye's syndrome.
For individuals who are already taking aspirin regularly, the FDA recommend limiting alcohol intake, as the combination of both can increase the risk of stomach bleeding.
People who are undergoing surgical or dental procedures should also inform their surgeon or dentist if they are taking aspirin regularly, as the drug may increase the risk for bleeding during surgery.
Our Knowledge Center article "What is aspirin? What is aspirin for?" provides further information on the health benefits and risks of the drug.