The value of a daily, low-dose aspirin regimen for some people has long been established. But, one of the most often discussed and debated topics about aspirin is ‘should I take it in the morning or evening?’

Recently I received a “pass-it-along” email reporting on a 2008 study by a cardiologist from the Mayo Clinic that was published in the Journal of the American College of Cardiology [1]. The email suggested that the study’s author recommended a nighttime consumption of low dose aspirin (81 mg or “baby” aspirin) is preferred over taking it in the morning. I’d never heard of a specific time of day aspirin use, so I decided to investigate.

According to the U.S. Centers for Disease Control and Prevention [2], taking a daily dose of aspirin can be useful for someone who has had a heart attack, stroke, angina or peripheral vascular disease or may be at risk for same. However, there are some instances where aspirin may not be appropriate as a daily regimen. Only a discussion with your doctor will determine if you should or should not take daily aspirin.

The recommendation of the American Heart Association is that people at high risk of heart attack take a daily low-dose of aspirin (again, only after consulting your doctor or health care provider) and that heart attack survivors regularly take low-dose aspirin.

But, that still leaves the question of what time of the day to take aspirin if you are taking it daily.

Aspirin tablets(100921)Credit: Mayo ClinicDay Time or Nighttime?

The article/study that was passed along to me [1], was conducted not to determine the time of day to take aspirin, but had to do with sufferers of sleep apnea that had a heart attack at night. It was only in that specific circumstance that nighttime use of aspirin was suggested in this study.

In another study in 2011, conducted by scientists in Spain [3], it was reported that a small dose of aspirin taken at night could reduce the risk of heart attack or stroke in people with high blood pressure – more so than if aspirin were taken in the morning. As reported in many media stories, the researchers determined that aspirin lowers blood pressure to normal for up to 24 hours, but the effect only happens when aspirin is taken at night.

However, on closer inspection of the study itself, the research indicated it was hypertension medication – not necessarily only aspirin – that had the nighttime effect. The researchers had tested more than 660 patients and had some of them take their medication at bedtime and others in the morning. Following up with the patients after more than five years, the researchers found that the patients who took their medicine at night had an adjusted risk for cardiovascular events that was approximately one-third that of patients who took all medications in the morning. Therefore, the researchers concluded that for patients with hypertension taking their medicine at night was better. But, even the researchers acknowledge they could not determine why aspirin or other medications might work better at night (although they surmise it may have something to do with the slower production of hormones or other body substances). And, they admit, timing the best moment to give a drug is an emerging science at this point.

Dr. Oz Chimes In

But even the inimitable Dr. Oz suggests taking “2 baby aspirin every night before bed” (although no studies, nor the recommendations by the American Heart Association suggest taking more than one low dose aspirin per day).

Indeed, some medications are specifically prescribed to be taken in the morning and/or with food. Additionally, the Spanish study was meant to examine aspirin in the context of hypertension. Many people, however, are prescribed aspirin for its anti-clotting capabilities linked to heart disease and stroke in high-risk patients.

James Black, a pharmacist in North Carolina, suggests it is better to take aspirin in the morning. He says he finds it easier for patients to remember to take it in the morning and that taking it with a meal means there is less chance of it interacting with other medicines (he says aspirin is not as effective when taken with other medicines). This is particularly the case, he says, because many people who take aspirin are older and some are on anti-inflammatory medicines like ibuprofen. “You need to take aspirin at least 30 minutes before taking an anti-inflammatory,” he says. He added that if you take aspirin right before or right after the anti-inflammatory medicine the aspirin is not able to bind with the protein in the blood it needs to connect with in order to be effective because the anti-inflammatory binds with that same protein.

Platelets The Key

Still seeking to gain a higher degree of certainty about taking aspirin at night or in the morning, researchers at Harvard University, explained that platelets (the element in blood responsible for clotting) are so sensitive to aspirin that a single 81-mg dose will inhibit the stickiness of all the platelets in your body. But platelets are always being removed from your blood and replaced by new platelets. That’s why it is necessary to take aspirin daily (although the Physicians' Health Study conducted in the 1990s at Brigham and Women’s Hospital in Boston suggested taking aspirin every other day is sufficient).

The Harvard scientists, noting the results of the Spanish study, also suggests bedtime aspirin is better. But, they also acknowledge that most people find it easier to remember to take their medications first thing in the morning. Accordingly, the researchers conclude that taking aspirin consistently may be more important than any concern over the time of day it is taken.

That seems to reflect most of the common scientific wisdom; taking aspirin if your physician prescribes it for you is important. When you take it is of secondary importance, if at all. Advocates of bedtime or morning consumption of aspirin can find support for their view in many forums, discussions, and medical opinions. Current research might seem to support nighttime aspirin consumption – but even that research is tentative and acknowledges the need for additional research, something that has not yet happened.

So, the bottom line is – check with your doctor and if he/she suggests aspirin might be good for you take it regularly and consistently. Don’t be too concerned with the morning/nighttime debate unless your doctor has a good and specific reason for you to do one or the other.


[1] Day-night variation of acute myocardial infarction in obstructive sleep apnea. Journal of the American College of Cardiology. 2008 Jul 29;52(5):343-6.


[3] Bedtime dosing of antihypertensive medications reduces cardiovascular risk in CKD. Journal of the American Society of Nephrology. 2011 Dec, 22(12):2313-21.