Coffee on an Empty Stomach: Is It Bad? What Research Shows

Coffee on an empty stomach is fine for many people, but it does a few things worth knowing. Coffee stimulates gastrin and stomach acid, and heartburn is the symptom people report most after drinking it (Boekema et al., 1999). In a crossover study, strong black coffee about an hour after waking raised the blood sugar and insulin response to a glucose drink taken 30 minutes later (Smith et al., 2020). Caffeine also raises cortisol, though less in people who drink it every day (Lovallo et al., 2005). This guide explains each finding and simple ways to make a morning cup sit better.

It is educational, not medical advice. If coffee regularly upsets your stomach, talk with your health care provider.

Key Takeaways

• Stomach acid: coffee stimulates gastrin release and gastric acid secretion (Boekema et al., 1999).
• Not the acidity alone: coffee's effects on the gut cannot be put down to its volume, acidity or caffeine alone (Boekema et al., 1999).
• Blood sugar: about 300 mg of caffeine as strong black coffee before a glucose drink raised peak glucose and insulin in 29 healthy adults (Smith et al., 2020).
• Cortisol: caffeine raised cortisol across the day after a break from caffeine; daily intake reduced, but did not remove, the rise (Lovallo et al., 2005).
• Upset stomach is a sign of too much: the FDA lists upset stomach and nausea among signs of too much caffeine (FDA).

Is It Bad to Drink Coffee on an Empty Stomach?

Not for everyone. A review of coffee and the gut found no link between coffee and indigestion in general, but it did find that coffee promotes acid reflux and that heartburn is the most frequently reported symptom after coffee drinking (Boekema et al., 1999). Whether your first cup comes before or after food, the same coffee reaches the same stomach; what changes is whether there is food there with it. If coffee on an empty stomach feels fine for you, the research here does not say you need to stop. If it gives you heartburn, a sour stomach or the jitters, the steps further down are worth trying.

Coffee and Stomach Acid

Coffee stimulates the release of gastrin, a hormone that tells the stomach to make acid, and it stimulates gastric acid secretion itself (Boekema et al., 1999). Interestingly, the review found that these effects cannot be explained by coffee's volume, acidity or osmolality, and that caffeine cannot fully account for them either, which means other compounds in coffee play a part (Boekema et al., 1999). That is one reason switching to decaf does not always settle things for people who are sensitive.

Coffee also gets the lower gut moving: in some people it increases activity in the last part of the colon within 4 minutes, with an effect comparable to a 1,000 calorie meal (Boekema et al., 1999). Many people notice this as needing the bathroom soon after a morning cup.

Coffee Before Breakfast and Blood Sugar

In a randomized crossover study, 29 healthy adults had a glucose drink in the morning on three occasions: after a normal night, after a night woken every hour, and after the broken night plus strong black coffee, about 300 mg of caffeine, taken about an hour after waking and 30 minutes before the glucose drink. The broken sleep alone did not change their glucose or insulin responses, but the coffee did: peak glucose and insulin were higher, and the researchers concluded that a strong caffeinated coffee before eating can be expected to reduce glucose tolerance (Smith et al., 2020).

The study did not test coffee taken with or after food, so it cannot say whether eating first removes the effect. Its practical message is simply that a very strong coffee before breakfast changes how your body handles the next meal for a while. For more on what drives blood sugar swings, see blood sugar spikes.

Coffee and Cortisol

Caffeine raises cortisol, the body's main stress hormone. In a double-blind trial, 96 men and women were tested after 5 days on capsules giving 0, 300 or 600 mg of caffeine a day. After 5 days without caffeine, caffeine doses caused a strong rise in cortisol across the test day; in people taking caffeine daily, the cortisol response was smaller but did not disappear (Lovallo et al., 2005). The study gave caffeine in capsules at set times, so it does not answer whether drinking coffee before or after breakfast makes a difference. For background, see what is cortisol.

How to Make Morning Coffee Easier on Your Stomach

• Eat something first or with it: the blood sugar finding came from strong coffee taken before a glucose drink, with no food first (Smith et al., 2020).
• Make it smaller or weaker: the study used about 300 mg of caffeine (Smith et al., 2020); an 8 oz cup of brewed coffee has about 95 mg (USDA FoodData Central).
• Watch the total: upset stomach, nausea and jitters are signs of too much caffeine (FDA).
• Try tea some mornings: brewed black tea has about 47 mg of caffeine per 8 oz, about half of coffee (USDA FoodData Central; USDA FoodData Central).
• Notice whether decaf helps: caffeine cannot fully account for coffee's effects on the gut, so decaf may help some people less than expected (Boekema et al., 1999).

Coffee, Tea and Caffeine at a Glance

Morning drink	Caffeine	Source
Brewed coffee, 8 oz	about 95 mg	USDA
Regular brewed coffee, 12 oz	113 to 247 mg	FDA
Brewed black tea, 8 oz	about 47 mg	USDA
Black tea, 12 oz	71 mg	FDA
Decaf coffee, 8 oz	2 to 15 mg	FDA

The 8 oz figures are calculated from USDA values of 40 mg of caffeine per 100 g of brewed coffee (USDA FoodData Central) and 20 mg per 100 g of brewed black tea (USDA FoodData Central); the other figures are FDA typical amounts (FDA).

How Much Coffee Is Too Much?

For most adults, the FDA cites 400 mg of caffeine a day, about two to three 12 oz cups of coffee, as an amount not generally associated with negative effects, while noting that sensitivity varies widely (FDA). If your morning coffee leaves you shaky or wired and then tired by midday, see caffeine crash and how much caffeine is too much. To cut back, our list of coffee alternatives and tea vs coffee can help.

Where Our Products Fit

Some people pair caffeine with L-theanine: in a placebo-controlled study, 50 mg of caffeine with 100 mg of L-theanine improved speed and accuracy on an attention switching task (Owen et al., 2008). Theanine Nasal Spray gives 36 mg of L-theanine per serving and is caffeine-free, so it adds no caffeine to your morning. The Energy Stack combines NAD+ Nasal Spray, Forage and Methyl B-12 Nasal Spray in one daily energy routine. Read more in L-theanine and caffeine, on our L-theanine ingredient page and in the Non-Stimulant Energy and Focus hub.

Frequently Asked Questions

Is it OK to drink coffee on an empty stomach?

For many people, yes. Coffee does raise stomach acid and is linked with heartburn in some people (Boekema et al., 1999), so if it bothers you, have it with food.

Why does coffee on an empty stomach make me feel sick?

Coffee stimulates gastrin and stomach acid (Boekema et al., 1999), and the FDA lists upset stomach and nausea among signs of too much caffeine (FDA).

Does coffee on an empty stomach raise blood sugar?

In one study, strong black coffee before a glucose drink raised the peak glucose and insulin response in healthy adults (Smith et al., 2020).

Does coffee raise cortisol?

Yes. Caffeine raised cortisol in a controlled trial, and daily intake made the rise smaller without removing it (Lovallo et al., 2005).

Is decaf easier on an empty stomach?

Possibly, but not always: caffeine cannot fully account for coffee's effects on the gut (Boekema et al., 1999).

Should I drink water before coffee?

Water is a fine way to start the day, but the studies here did not test it, so there is no research answer on whether it changes coffee's effects.

Is tea better than coffee on an empty stomach?

Tea has less caffeine, about 47 mg per 8 oz of black tea against about 95 mg for coffee (USDA FoodData Central; USDA FoodData Central). The review here looked at coffee, not tea.

Why does coffee make me need the bathroom?

In some people coffee increases activity in the lower colon within 4 minutes (Boekema et al., 1999).

Sources

1. Boekema PJ, Samsom M, van Berge Henegouwen GP, Smout AJ. Coffee and gastrointestinal function: facts and fiction. A review. Scand J Gastroenterol Suppl. 1999. PubMed 10499460
2. Smith HA, Hengist A, Thomas J, et al. Glucose control upon waking is unaffected by hourly sleep fragmentation during the night, but is impaired by morning caffeinated coffee. Br J Nutr. 2020. PubMed 32475359
3. Lovallo WR, Whitsett TL, al'Absi M, et al. Caffeine stimulation of cortisol secretion across the waking hours in relation to caffeine intake levels. Psychosom Med. 2005. PubMed 16204431
4. Owen GN, Parnell H, De Bruin EA, Rycroft JA. The combined effects of L-theanine and caffeine on cognitive performance and mood. Nutr Neurosci. 2008. PubMed 18681988
5. U.S. Food and Drug Administration. Spilling the Beans: How Much Caffeine Is Too Much? FDA
6. U.S. Department of Agriculture. FoodData Central: Beverages, coffee, brewed, prepared with tap water (FDC 171890); Beverages, tea, black, brewed, prepared with tap water (FDC 173227). FoodData Central

Our products are not intended to diagnose, treat, cure or prevent any disease. This article is for education only and is not medical advice.