Caffeine and cortisol: does coffee raise your stress hormone?

Key takeaways

• In a double-blind trial of 96 healthy young adults, caffeine after five days of abstinence raised cortisol strongly across the test day.
• After five days of regular caffeine (300 or 600 mg a day), the cortisol response to a 9 a.m. dose was gone, but a 1 p.m. dose still raised cortisol.
• The authors’ conclusion: cortisol responses to caffeine are reduced, but not eliminated, in daily users.
• The study did not test “wait 90 minutes after waking” advice, and did not test whether caffeine affects belly fat or weight.

What the main caffeine and cortisol trial measured

One study that tested this directly is a 2005 trial by Lovallo and colleagues in Psychosomatic Medicine. It reported on 96 healthy young adults who completed it, 48 men and 48 women, in a double-blind crossover design over four weeks.

In each week, participants avoided dietary caffeine for five days and instead took capsules that gave them 0, 300 or 600 mg of caffeine a day in three doses, with the order of the weeks randomized. On the sixth day they took capsules containing either 0 mg (a placebo) or 250 mg of caffeine at 9 a.m., 1 p.m. and 6 p.m., and the researchers measured cortisol in saliva repeatedly across the day.

This design let the researchers compare the same people when they were caffeine-free and when they were used to caffeine, which is the comparison that matters for someone who drinks coffee every day.

Does coffee raise cortisol if you drink it every day?

Less than if you don’t. After five days without caffeine, the caffeine doses caused a robust rise in cortisol across the test day. After five days of 300 or 600 mg a day, the 9 a.m. dose no longer raised cortisol at all. Cortisol was raised again between 1 p.m. and 7 p.m., after the 1 p.m. dose, and fell back to control levels during the evening samples.

The authors’ summary is that cortisol responses to caffeine are reduced, but not eliminated, in healthy young men and women who consume caffeine daily. So for a regular coffee drinker, the morning cup appears to have little cortisol effect, while extra caffeine later in the day may still have some.

Note what the study used: caffeine capsules, not coffee, and healthy young adults, not people with health conditions. Other parts of the body respond too. In a study of 102 light caffeine users, caffeine raised blood pressure, and MedlinePlus also lists raised blood pressure among caffeine’s effects. If caffeine makes you feel anxious or on edge, see why coffee makes you anxious.

The cortisol argument for delaying your first coffee

A popular idea says you should wait 90 minutes or more after waking before your first coffee, because cortisol is already high in the morning. We could not find a study that tests this. The Lovallo trial measured how caffeine changes cortisol; it did not compare drinking coffee at different times after waking, and it did not report effects on energy, focus or sleep.

If anything, its finding that regular users lose the cortisol response to a morning dose does not support the idea that a morning coffee piles more cortisol on top. Our page on waiting 90 minutes to drink coffee looks at the other reasons people give, and the best time to drink coffee guide covers timing for sleep.

What the caffeine and cortisol research does not show

Claims about caffeine, cortisol and weight, such as “cortisol belly”, are not supported by the study above: it measured salivary cortisol on a single test day in each week and did not test whether caffeine changes weight or body fat. We make no claim about caffeine and body fat. The trial also tells us nothing about people under long-term stress, people with hormone conditions, or pregnancy.

Dose and timing for sleep are worth keeping in mind too. EFSA says single doses up to 200 mg raise no safety concerns for healthy adults, but even 100 mg may affect sleep in some adults when taken close to bedtime. Use the caffeine cutoff calculator to find your latest time.

Common questions