Aspirin can affect blood glucose readings in two distinct ways: it may interfere with the accuracy of certain testing devices, and it can genuinely lower your blood sugar through its effects on insulin. The practical impact depends on the type of test, the dose of aspirin, and whether you’re using a fingerstick meter, a continuous glucose monitor, or getting lab work like an HbA1c.
How Aspirin Affects Glucose Monitor Readings
When your body breaks down aspirin (acetylsalicylic acid), it produces metabolites called salicylic acid and gentisic acid. These byproducts are electroactive, meaning they can interact with the chemical sensors in glucose test strips and continuous glucose monitors. The result is a reading that doesn’t reflect your actual blood sugar.
The FreeStyle Libre 14-day sensor, for example, carries a manufacturer warning that salicylic acid “may slightly lower sensor glucose readings,” with the degree of inaccuracy depending on how much aspirin you’ve taken. Gentisic acid, another aspirin metabolite, has been flagged as an interferent for certain fingerstick meters as well. In both cases, the readings tend to skew lower than your true glucose level, not higher.
Dexcom sensors don’t carry the same explicit labeling about aspirin, but the concern isn’t fully settled. At least one clinical study for the Roche Accu-Chek SmartGuide CGM system excluded participants taking aspirin entirely, suggesting manufacturers take the potential for interference seriously even when it isn’t listed on the label.
Aspirin’s Real Effect on Blood Sugar
Beyond test interference, aspirin and related salicylates genuinely lower blood glucose. This isn’t a measurement error. It’s a pharmacological effect. A randomized, placebo-controlled trial published in Nature Reviews Endocrinology found that salicylates increase insulin levels in the blood, which in turn brings glucose down. The glucose-lowering effect occurs at both fasting and after meals.
Animal research reinforces this. In one study, mice given a low dose of aspirin comparable to a human dose of about 70 mg per kilogram of body weight had significantly lower blood glucose than untreated mice with diabetes (383 mg/dL versus 494 mg/dL). While animal doses don’t translate directly to humans, the finding is consistent: aspirin has a measurable effect on blood sugar itself, not just on the tools measuring it.
This means that if you take aspirin regularly and your glucose readings seem lower than expected, part of that drop may be real. Separating the genuine glucose-lowering effect from device interference is difficult without lab verification.
What About HbA1c Tests?
The HbA1c test measures how much sugar has attached to your red blood cells over the past two to three months. Aspirin can interfere with this test too, but the picture is complicated. Chronic aspirin use in large doses can cause a chemical change called acetylation of hemoglobin, which some lab assays misread as elevated HbA1c, pushing your result falsely higher. At the same time, other reports have found that chronic aspirin use can falsely decrease HbA1c readings through a similar mechanism affecting different assay types.
The direction of the error depends on the specific laboratory method used to run your test. You won’t typically know which assay your lab uses, but if your HbA1c results seem inconsistent with your daily glucose readings, regular aspirin use is one factor worth discussing with whoever ordered the test.
Does a Daily Baby Aspirin Matter?
Most people asking this question are taking a standard low-dose (81 mg) aspirin for heart health, which is commonly prescribed for people with diabetes who are at higher cardiovascular risk. At this dose, the device interference effects tend to be small. The FreeStyle Libre labeling describes the impact of salicylic acid as “slight,” with greater inaccuracy tied to larger amounts consumed.
That said, “slight” still matters if you’re making insulin dosing decisions based on a CGM reading that’s a few points lower than reality. The real glucose-lowering effect of aspirin also exists at low doses, though it’s more modest than what you’d see with high-dose salicylate therapy. For most people on baby aspirin, the combined impact is unlikely to cause dangerous misreadings, but it’s a known variable in your numbers.
Practical Steps for Accurate Readings
If you use a continuous glucose monitor and take aspirin regularly, periodic fingerstick checks with a meter that doesn’t list salicylic acid as an interferent can help you spot discrepancies. When you’re getting lab work done, make sure aspirin is listed among your current medications so results can be interpreted in context.
Timing also matters for fingerstick tests. Aspirin metabolites peak in your blood within a few hours of taking a dose, so testing at different times relative to when you take your aspirin can reveal whether your readings shift. If you notice that your glucose always reads lower shortly after your aspirin dose, interference is a likely contributor. Keeping a simple log of when you take aspirin and when you test can help identify patterns that would otherwise be invisible in the numbers alone.