Coffee Before or After Breakfast: What Research Actually Shows

Reviewed and refreshed in May 2026 by Mira Karenko. This article reflects current peer-reviewed research and is provided for general information only.

Most of us reach for coffee before we reach for food. Then someone in your feed claims that drinking coffee on an empty stomach wrecks your cortisol, spikes your blood sugar, or eats away at your stomach lining. So which is it? Is morning coffee before breakfast a problem, or is it fine?

For most healthy adults, drinking coffee before breakfast is fine. There is one well-designed study showing that strong coffee on a poor night’s sleep can dent your glucose response to breakfast. The popular cortisol claim, on the other hand, has been stretched well past what the original research actually says. Here is what the evidence shows, and where it pays to be careful.

Quick answer

• For most healthy adults, coffee before breakfast does not cause harm.
• Strong coffee on top of a bad night’s sleep can blunt your blood sugar response to breakfast (Smith et al., 2020).
• The “wait 90 minutes after waking for cortisol” advice is not supported by clinical evidence in healthy people.
• Coffee does raise gastric acid, which can bother people with reflux, gastritis, or ulcers. Eating first helps.
• If you have type 2 diabetes, GERD, anxiety, or are pregnant, the timing of coffee matters more for you than for the average drinker.

Medical disclaimer. The information here is not medical advice. If you have a chronic condition, take medication, or are pregnant, talk to your doctor about how coffee fits into your routine.

The Bath glucose study: the strongest evidence we have

The most cited research on this question comes from the University of Bath. In a 2020 study in the British Journal of Nutrition, Smith and colleagues had 29 healthy adults complete three overnight conditions: a normal night of sleep followed by a sugary drink in the morning, a fragmented night followed by the same drink, and a fragmented night followed by strong black coffee about 30 minutes before the drink (Smith et al., 2020).

Disrupted sleep alone did not impair glucose or insulin responses. But adding strong black coffee before breakfast raised the blood glucose response by roughly 50% compared with eating breakfast without the coffee first. The order mattered. Coffee before food, in people who had slept badly, made their bodies handle the carbohydrates in breakfast less efficiently.

Two caveats. The dose was strong (about 300 mg of caffeine, roughly two large brewed cups), and the test breakfast was deliberately sugary. Whether the same effect shows up with a smaller cup followed by a balanced meal is not yet clear. But the signal is real and lines up with older research showing caffeine can reduce insulin sensitivity acutely. If you have prediabetes, type 2 diabetes, or your fasting glucose runs high, strong coffee right before a carb-heavy breakfast is the scenario most likely to matter. For more, see our guide to coffee and diabetes.

The cortisol claim, examined

You have probably seen the advice: do not drink coffee for the first 90 minutes after you wake up because your cortisol is high and caffeine will blunt its natural rhythm. The research it leans on does not actually support the recommendation.

Cortisol does peak within 30 to 45 minutes of waking, and caffeine raises cortisol levels, especially in people who do not consume caffeine regularly (Lovallo et al., 2005, Psychosomatic Medicine). But Lovallo’s group also showed that habitual coffee drinkers develop tolerance to this cortisol effect within days to weeks. By the time you are a daily coffee drinker, the cortisol bump from your morning cup is small.

No clinical trial has shown that drinking coffee during the natural cortisol peak causes harm or “blunts” the awakening response in any meaningful way. The 90-minute rule comes from a social-media interpretation of basic physiology, not from a study showing that people who wait 90 minutes feel or sleep better than people who do not. If waiting feels better for you personally, that is a fine reason to do it. It is not a research-based requirement.

Coffee and your stomach

Coffee stimulates gastric acid secretion. Cohen and Booth showed in the New England Journal of Medicine back in 1975 that both regular and decaffeinated coffee increased gastric acid output and lowered the pressure of the lower esophageal sphincter (Cohen and Booth, 1975). Decaf did this too, which tells us caffeine is not the only culprit. Compounds called chlorogenic acids also stimulate acid production.

For most healthy people, this extra acid does nothing noticeable. For people with gastritis, ulcers, or GERD, coffee on an empty stomach can trigger burning, nausea, or heartburn an hour later. Eating something first puts a buffer in your stomach, dilutes the acid, and reduces contact time with your stomach lining. If you wake up with reflux or stomach discomfort, eating a small protein-and-fat meal before your first cup is a reasonable experiment. See our guide to coffee and acid reflux for which roasts and brewing methods are gentler.

Who should be more careful about timing

For an average healthy adult who drinks one or two cups in the morning, the order rarely makes a measurable difference. These groups should pay closer attention:

• People with type 2 diabetes or prediabetes. The Bath study suggests strong coffee before a high-carb breakfast can elevate post-meal glucose. Drinking coffee with or after the meal, or choosing a lower-carb breakfast, may be preferable.
• People with GERD, gastritis, or ulcers. Coffee on an empty stomach amplifies acid contact time. Eating first helps. Cold-brew and low-acid roasts may also be gentler.
• People with anxiety disorders or caffeine sensitivity. Faster absorption on an empty stomach can mean sharper jitters and palpitations. A meal first smooths the curve.
• Pregnant women. The American College of Obstetricians and Gynecologists recommends limiting caffeine to under 200 mg per day. See our article on coffee during pregnancy.
• People on certain medications. Levothyroxine, some osteoporosis drugs, and iron supplements absorb less well when taken with coffee. Take the medication, wait 30 to 60 minutes, then have your coffee.

Practical recommendations

1. Drink water first. You wake up mildly dehydrated. A glass of water (about 240 ml or 8 oz / 1 cup) takes the edge off before you add a stimulant.
2. If you are healthy and feel fine on empty-stomach coffee, carry on. There is no clinical reason to change.
3. If you have any of the conditions above, eat something small first. A few bites of protein and fat is enough to change the curve.
4. If you sleep poorly the night before, push coffee until after a real breakfast. This is where the Bath evidence is strongest.
5. Pay attention to how you actually feel. If empty-stomach coffee leaves you anxious or shaky, that is data. Eat first.

For more on how much coffee is reasonable in a day, see our article on how much coffee is too much.

Frequently asked questions

Is it bad to drink coffee on an empty stomach?

For healthy adults without digestive or metabolic conditions, no. It hits faster and can feel sharper, but it does not cause measurable harm in clinical research. If you have GERD, gastritis, anxiety, or diabetes, eating first is usually better.

Should I really wait 90 minutes after waking to drink coffee?

There is no clinical evidence supporting this. The advice is based on a stretched interpretation of cortisol research. If you drink coffee daily, your body has already adapted to the small cortisol effect. Wait if it feels better, but do not treat it as a rule.

Does coffee before breakfast spike blood sugar?

Strong coffee on a poor night’s sleep, followed by a sugary breakfast, raised post-meal glucose by about 50% in the 2020 University of Bath study (Smith et al., 2020). For people with normal sleep and a balanced breakfast, the effect is much smaller. People with diabetes or prediabetes should consider drinking coffee with or after the meal.

Should I take my thyroid medication with coffee?

No. Coffee significantly reduces absorption of levothyroxine. Take the medication on an empty stomach with water, then wait at least 30 to 60 minutes before drinking coffee. Check the instructions on your specific medication.

Is coffee with breakfast better than coffee alone?

For people with reflux, anxiety, or blood sugar issues, yes. The food slows absorption, buffers stomach acid, and reduces the sharpness of the caffeine peak. For healthy people without those issues, either pattern works.

Sources

• Smith HA, Hengist A, Bonson DJ, et al. “Glucose control upon waking is unaffected by hourly sleep fragmentation during the night, but is impaired by morning caffeinated coffee.” British Journal of Nutrition, 124(10), 2020.
• Lovallo WR, Whitsett TL, al’Absi M, Sung BH, Vincent AS, Wilson MF. “Caffeine stimulation of cortisol secretion across the waking hours in relation to caffeine intake levels.” Psychosomatic Medicine, 67(5), 2005.
• Cohen S, Booth GH Jr. “Gastric acid secretion and lower-esophageal-sphincter pressure in response to coffee and caffeine.” New England Journal of Medicine, 293(18), 1975.
• Boekema PJ, Samsom M, van Berge Henegouwen GP, Smout AJPM. “Coffee and gastrointestinal function: facts and fiction. A review.” Scandinavian Journal of Gastroenterology Supplement, 230, 1999.
• American College of Obstetricians and Gynecologists. “Moderate caffeine consumption during pregnancy.” Committee Opinion No. 462, reaffirmed 2020.
• European Food Safety Authority (EFSA). “Scientific Opinion on the safety of caffeine.” EFSA Journal, 13(5), 2015.
• Mayo Clinic. “Caffeine: How much is too much?” Patient education materials.

This article is for general information and is not a substitute for medical advice. If you have diabetes, GERD, anxiety disorders, are pregnant, or take prescription medication, talk to your doctor about how coffee timing fits your routine. Last reviewed May 2026.