For some, the day doesn't start with the first cup of coffee. But for others, this ritual, known for bringing focus and energy, can cause a racing heart, nervous hands and a vague sense of dread that lingers long after the caffeine buzz has worn off.
Here's why caffeine can cause anxiety, what caffeine does inside the body, and why some people are much more sensitive to it than others.
15–45 minutes after you drink a cup of coffee, caffeine passes through the bloodstream and reaches the brain. There it blocks adenosine receptors, the nerve “brakes” that promote calmness and drowsiness. This blockade results in the release of dopamine and norepinephrine: two neurotransmitters that promote “increased alertness, increased arousal, and decreased fatigue,” says Dr. Amin Yehya, a cardiologist at Sentara Health in Virginia. But in large quantities, dopamine and norepinephrine also increase heart rate and blood pressure and activate areas of the brain involved in sensing threat. This is the same system that controls the body's stress response and can contribute to anxiety and restlessness.
Dr. John Higgins, a cardiologist at UTHealth Houston, notes that caffeine's most immediate effects are neurological. When caffeine blocks adenosine receptors and “removes this brake, neurons fire faster, cortical firing increases, and blood vessels constrict slightly, increasing blood pressure and creating physical sensations that many people interpret as nervousness.”
Read more: 6 migraine symptoms that aren't headaches
This sudden state of activation can feel like clarity and motivation for some, and anxiety for others. 2023 study published in the journal Clinical autonomous studies shows that this increased arousal can almost perfectly mimic the physical symptoms of anxiety, which helps explain why the line between “energetic” and “anxious” is so thin.
Caffeine can also cause anxiety in other ways. This activates hypothalamic-pituitary-adrenal axis (HPA), increasing cortisol and adrenaline, which are the main stress hormones in the body. “Caffeine stimulates the same hormonal pathways that are activated during stress,” Yehya says.
Kevin Woods, director of science at Brain.fm, says caffeine's promise to improve focus can be misleading. “Your prefrontal cortex, where focus and decision-making occurs, doesn't actually work better in fight-or-flight mode,” he says. “You may feel excited, but that's not the same as being mentally sharp.”
Not everyone experiences anxiety after drinking coffee, and genetics plays a role in determining who does.
Variations in the genes alter how adenosine and dopamine receptors work in the brain, and some mutations may slow the liver's metabolism of caffeine, Yehya said. People with these gene variants process caffeine more slowly, allowing it to linger in the bloodstream and prolonging its stimulant effects, which can contribute to feelings of greater anxiety.
That's why “the same cup of coffee can make different people feel completely different,” says Higgins.
US Food and Drug Administration recommends no more than 400 mg of caffeine per day—about two to three 12-ounce servings. cups of brewed coffee for most healthy adults. But this limit is not hard and fast. “There is no specific amount of caffeine that always causes anxiety,” Yehya says.
Genes are not the only factor. So does a person's caffeine tolerance and health, says Dr. Ajay Pillai, an electrophysiologist at VCU Health Pauley Heart Center. “Caffeine consumption can dramatically increase your heart rate and blood pressure by as much as 5 to 10 mmHg. Art.,” he says. “This effect may be more pronounced in people with hypertension or those who are already stressed.”
Read more: What happens to the plastic in disposable coffee capsules?
For sensitive people, even one cup may be too much, while others can tolerate more without ill effects. “Know your body and limit your intake,” advises Dr. Mohanakrishnan Sathyamurthy, chairman of the department of internal medicine at Texas Christian University Burnett Medical School. “Consume light to moderate and be aware of the amount of caffeine in your favorite beverages.”
Lack of sleep, chronic stress, and hormonal fluctuations can increase the effects of caffeine. “When the body is already under stress, caffeine can exacerbate this reaction,” says Dr. Sogol Ash, a functional and preventive medicine physician and medical consultant for vitamin patch company Barrière. “Poor sleep, hormonal fluctuations and anxiety increase baseline levels of cortisol and adrenaline, leaving the nervous system in an elevated state.” Add caffeine and the effect becomes stronger.
Lack of sleep fundamentally changes how caffeine interacts with the brain.
“When you run on empty, your prefrontal cortex is already damaged,” Woods says. “Caffeine creates the illusion of alertness without restoring actual cognitive function. You may feel alert, but your ability to concentrate remains impaired.”
Women taking hormonal contraceptives or who are pregnant may also metabolize caffeine more slowly.
The good news is that you don't have to give up coffee completely. “Moderate coffee consumption—about two to three cups per day—is generally safe,” Yehya says. However, time matters. Avoiding caffeine in the afternoon or evening helps protect sleep quality, which directly impacts anxiety the next day.
Also, never drink coffee on an empty stomach, advises Ash. “Food helps slow the absorption of caffeine and buffers its effects on stress hormones,” she says. Combination of coffee with breakfast or milk-based products may blunt cortisol and blood sugar spikes. For those looking to reduce their exposure to caffeine, switching to semi-caffeinated, smaller portions, or decaffeinated coffee may help.
Read more: 7 polite phrases that are still worth saying
“Cooking method matters less than you think,” says Higgins.
Espresso packs majority caffeine per ounce (about 63 mg per serving), but 8 oz. a cup of coffee usually contains more caffeine – about 95 mg.
According to Higgins, cold and hot beer contain the same amount of caffeine when the ratio of coffee to water is appropriate. “The myth that cold brew is stronger comes from concentrated preparations that use a higher ratio of coffee to water,” he says. “Dilute it properly and the caffeine levels will normalize.”
Woods also encourages working with your body's natural rhythm. “Your cortisol naturally peaks around eight or nine in the morning, so waiting until mid-morning when it drops allows caffeine to complement your natural rhythm,” he says.
If you experience anxiety, palpitations or insomnia With coffee consumption in moderation, it may be time to reconsider your caffeine habit. “If someone's anxiety persists despite changes in caffeine intake, or their symptoms impair daily functioning, other medical conditions should be considered,” Yehya says. This may include anxiety disorders, cardiac arrhythmias, or thyroid problems.
Anxiety associated with caffeine is common and can be managed, but it can also be a clue to something deeper. “Talk to your doctor and include caffeine use in your medical history,” says Satyamurthy. “It's easy to overlook, but it could be an important piece of the puzzle.”
Ultimately, the answer isn't to give up coffee entirely, but to understand your body's relationship with it. For some, this means switching to decaf; for others, it means adjusting timing, food, or quantity. “Caffeine is not the enemy,” Woods says. “The goal is to work with the brain, not against it.”
