For millions of Americans, the morning coffee ritual comes with an unpleasant side effect: racing thoughts, shaky hands, a pounding heart, and that unmistakable feeling of being overstimulated.

Now, new research from Everyday Dose suggests those symptoms may have less to do with caffeine tolerance and more to do with genetics.

A nationwide survey of 2,974 weekly U.S. coffee drinkers, conducted independently by Quantix Partners and commissioned by functional coffee company Everyday Dose, found that 36% of coffee drinkers experience caffeine-induced jitters on a regular basis. In other words, more than one in three Americans may be genetically predisposed to react poorly to their daily cup of coffee.

The findings point toward a growing body of research surrounding the CYP1A2 gene, often referred to as the “Jitter Gene,” which plays a major role in determining how quickly the body metabolizes caffeine.

Why Coffee Affects People Differently

Everyone knows someone who can drink an espresso after dinner and fall asleep without a problem. Others feel anxious, shaky, or wired after a single cup.

According to researchers, the difference often comes down to variations in the CYP1A2 gene.

This gene regulates the production of an enzyme responsible for breaking down caffeine in the liver. People with certain genetic variants metabolize caffeine quickly, while others process it much more slowly.

Researchers have identified a specific genetic marker known as rs762551 that influences caffeine metabolism:

• A/A variant: Fast metabolizers who clear caffeine efficiently and typically experience fewer side effects.
• C/C variant: Slow metabolizers who process caffeine more slowly and often experience stronger, longer-lasting effects.
• A/C variant: Intermediate metabolizers who fall somewhere in between.

For slow metabolizers, a standard cup of coffee can lead to elevated caffeine levels that linger for hours, increasing the likelihood of jitters, anxiety, sleep disruption, and rapid heartbeat.

Younger Adults Are Feeling It the Most

One of the most striking findings from the survey was the dramatic age gap in caffeine sensitivity. Among adults aged 18 to 24, 58% reported experiencing coffee jitters. Among adults aged 65 and older, that figure dropped to just 12%.

Researchers suggest several factors may explain the difference. Younger adults tend to experience higher baseline anxiety levels, more irregular sleep schedules, and greater exposure to stress. Sleep deprivation alone can amplify the perceived effects of caffeine, making even moderate amounts feel overwhelming.

At the same time, younger consumers often consume caffeine from multiple sources throughout the day, including energy drinks, pre-workouts, sodas, and specialty coffee beverages.

The result is a generation that may be consuming more caffeine than ever while simultaneously being more vulnerable to its side effects.

Americans Are Already Changing Their Coffee Habits

The survey suggests many coffee drinkers are actively trying to reduce caffeine-related discomfort. Among those who experience jitters:

• 67% have reduced their coffee intake
• 66% have considered switching to lower-jitter alternatives
• 50% spread caffeine consumption throughout the day
• 47% only drink coffee alongside food
• 41% continue to tolerate jitters because they feel they need the energy boost
• 34% choose lower-caffeine blends

The data reveals a growing disconnect between people’s desire for energy and their ability to comfortably tolerate traditional coffee.

The Rise of “Calm Energy”

As awareness around caffeine sensitivity grows, many consumers are experimenting with alternatives designed to deliver energy without the crash, anxiety, or overstimulation.

Among survey respondents who experience caffeine sensitivity:

• 64% have tried tea
• 55% have tried decaf coffee
• 38% have tried matcha
• 22% have tried mushroom coffee
• 18% have tried L-theanine supplementation

This trend reflects broader growth in the functional beverage market, where products combining lower caffeine doses with ingredients designed to support focus and mood have become increasingly popular.

Mushroom coffee and nootropic beverages have emerged as particularly fast-growing categories, appealing to consumers who want cognitive benefits without the traditional downsides of high caffeine intake.

What Is L-Theanine?

One ingredient receiving significant attention is L-theanine, an amino acid naturally found in tea leaves.

Research suggests L-theanine may promote a state of calm alertness by influencing neurotransmitter activity in the brain. When paired with caffeine, studies have shown it can help improve focus and attention while reducing some of the nervousness and overstimulation that caffeine can cause in sensitive individuals.

This combination has become a common feature in many functional coffee products aimed at consumers seeking smoother, more balanced energy.

Should You Get Tested?

The survey found that 72% of jitter-prone coffee drinkers want to better understand their caffeine genetics. As direct-to-consumer genetic testing becomes more accessible, interest in personalized nutrition and caffeine metabolism continues to grow.

While a genetic test cannot predict every aspect of how someone will respond to caffeine, it can provide insight into whether they are likely to be a fast or slow metabolizer.

For people who routinely experience jitters, anxiety, sleep disruption, or heart palpitations after drinking coffee, genetics may offer part of the explanation.

The Bottom Line

For decades, coffee tolerance was often viewed as something people could simply build over time.

Emerging research paints a more nuanced picture.

Genetic differences—particularly variations in the CYP1A2 gene—appear to play a significant role in determining how caffeine affects the body. For many people, feeling jittery after coffee may not be a sign of weakness or low tolerance at all. It may simply be the way their biology is wired.

With 36% of coffee drinkers reporting regular jitters and younger adults showing particularly high sensitivity, the findings highlight a growing demand for personalized approaches to caffeine consumption and a new generation of products designed to deliver energy without the unwanted side effects.

Study Details

The survey was conducted by Quantix Partners in August 2025 and included 2,974 U.S. adults who drink coffee at least weekly. The research was commissioned by Everyday Dose and examined coffee habits, caffeine sensitivity, coping behaviors, and interest in genetic testing related to caffeine metabolism.

References

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3. Yang A, Palmer AA, de Wit H. Genetics of caffeine consumption and responses to caffeine. Psychopharmacology. 2010;211(3):245-257.

4. Nehlig A. Interindividual differences in caffeine metabolism and factors driving caffeine consumption. Pharmacol Rev. 2018;70(2):384-411.

5. Amin N, et al. Genome-wide association analysis of coffee drinking suggests association with CYP1A1/CYP1A2 and NRCAM. Mol Psychiatry. 2012;17(11):1116-1129.