For most people, drinking coffee on an empty stomach is not harmful, but it can cause acid reflux, nausea, or jitters in sensitive people. Having it with food can help.
Is it harmful
For most people it is fine. Coffee raises stomach acid, but studies show it doesn’t cause ulcers.
Possible effects
- Heartburn or reflux.
- Nausea or jitters.
- Increased cortisol (small effect).
Who should be careful
People with GERD, ulcers or gastritis.
Tips
Eat something first, choose a darker roast or cold brew, and keep it under 400 mg of caffeine a day.
Acid and stomach
Coffee stimulates stomach acid production and the hormone gastrin. For most people, this is not harmful. Some people with reflux, gastritis or ulcers report more discomfort, though studies on causation are mixed.
Digestion
Coffee can stimulate bowel movements by activating the colon within minutes, in about 29% of people according to a small study. This is related to gastrin and the gastrocolic reflex.
Cortisol
Cortisol is naturally highest about 30 to 45 minutes after waking. Some experts suggest waiting 60 to 90 minutes after waking to drink coffee to avoid stacking on cortisol, but evidence for this is limited.
Blood sugar
A small study in the British Journal of Nutrition found that strong black coffee after a poor night’s sleep raised blood sugar response to breakfast by about 50%. Effects differ among people.
Who should be careful
- People with GERD, ulcers or gastritis.
- Those prone to anxiety or panic.
- People with irritable bowel syndrome.
- Pregnant women, limiting caffeine to below 200 milligrams a day.
- People with heart rhythm problems, as advised by a doctor.
Common effects
Jitters, nausea, heartburn and a fast heartbeat from caffeine on an empty stomach.
Caffeine limits
The FDA says 400 milligrams of caffeine daily (about 4 cups of brewed coffee) is generally safe for healthy adults.
Tips
- Eat something small with your coffee, such as toast or yogurt.
- Choose lower acid or cold brew coffee.
- Add milk.
- Drink water too.
- Reduce intake if symptoms occur.
Benefits
Large studies link moderate coffee drinking to a lower risk of type 2 diabetes, liver disease and Parkinson’s disease.
Stomach acid and cortisol claims
Coffee stimulates gastric acid secretion through caffeine and other compounds, and in some people it relaxes the lower esophageal sphincter, which can worsen heartburn. Studies have not shown consistent harm in healthy people who drink coffee on an empty stomach. People with gastritis, ulcers, reflux or irritable bowel syndrome often report more symptoms. Cortisol levels peak 30 to 45 minutes after waking, and a popular claim is that waiting 60 to 90 minutes before coffee improves its effect, but there is limited evidence for this.
Practical advice
If coffee upsets your stomach, drink it with food, choose a darker roast or cold brew, which some people tolerate better, or reduce the amount. Keep total caffeine to about 400 mg a day, roughly four 8 ounce cups, per the FDA. Large observational studies link moderate coffee drinking with lower risk of type 2 diabetes, Parkinson disease and some liver disease, but those benefits do not depend on timing. Pregnant women should limit caffeine to 200 mg. Talk to a doctor if you have frequent heartburn, stomach pain or black stools.
Based on data from the FDA and the Harvard T.H. Chan School of Public Health
