What is the addictive substance in tea and coffee?

December 16, 2025 •

3 min read

Over 90% of adults in the United States consume caffeine regularly, often through coffee and tea. But many people are unaware that the addictive substance in tea and coffee is caffeine, a psychoactive stimulant that creates a mild dependence in regular users.

Quick Summary

The addictive substance in tea and coffee is caffeine, a central nervous system stimulant. It creates dependence by blocking adenosine receptors in the brain, leading to increased alertness and a rewarding sensation. Regular consumption results in tolerance and physical withdrawal symptoms upon cessation.

Key Points

Caffeine is the addictive substance: The primary psychoactive compound in both tea and coffee is caffeine, a central nervous system stimulant.
Caffeine blocks adenosine receptors: Caffeine's addictive mechanism involves blocking adenosine receptors in the brain, preventing drowsiness and increasing neural activity.
Tolerance leads to higher consumption: Regular intake causes the brain to produce more adenosine receptors, leading to tolerance and the need for higher doses to achieve the same effect.
Withdrawal symptoms are a sign of dependence: Abrupt cessation of caffeine can trigger withdrawal symptoms like headaches, fatigue, and irritability, indicating physical dependence.
Tea's L-theanine modulates the effect: Unlike coffee, tea contains L-theanine, an amino acid that creates a more calming, sustained alertness by mitigating caffeine's jittery effects.
Moderation is key for health: While moderate intake is generally safe, excessive caffeine can cause anxiety, insomnia, and other health issues, and should be gradually reduced if dependence is a concern.
Caffeine levels differ by preparation: A cup of brewed coffee typically contains significantly more caffeine than a cup of black tea due to brewing method differences.

Understanding Caffeine: The Common Link

Caffeine, a natural central nervous system (CNS) stimulant found in coffee beans and tea leaves, is the most widely consumed psychoactive drug globally. It's known for boosting alertness and reducing fatigue. Regular, prolonged use of caffeine can lead to dependence and withdrawal.

The Mechanism of Caffeine's Effects

Caffeine affects the brain by blocking adenosine, a neurotransmitter that causes drowsiness. Caffeine is similar in structure to adenosine and occupies its receptors in brain cells. This blockage increases nerve activity and triggers the release of natural stimulants like adrenaline and dopamine. While the dopamine release is less intense than that from stronger drugs, it contributes to caffeine's rewarding effect and potential for dependency.

Developing Tolerance and Dependence

Consistent caffeine intake prompts the brain to increase adenosine receptors, leading to tolerance. This means a higher dose of caffeine is needed for the same stimulating effect. This cycle fosters physical dependence. When caffeine is stopped, the excess unblocked adenosine receptors become overstimulated, causing withdrawal symptoms.

The Experience of Caffeine Withdrawal

Caffeine withdrawal is a recognized condition with various symptoms. Symptoms typically appear 12–24 hours after the last dose, peak around 20–51 hours, and can last for several days to over a week, depending on typical intake. The intensity of withdrawal correlates with the dose and duration of regular use.

Common Withdrawal Symptoms

Headache: Often caused by blood vessel dilation in the brain.
Fatigue and Drowsiness: Occurs as adenosine receptors become active again.
Irritability and Depressed Mood: Reflects reliance on caffeine's mood effects.
Difficulty Concentrating: Due to disruption of the brain's stimulant balance.
Flu-like Symptoms: May include nausea or muscle aches.

The Difference in Caffeine Between Tea and Coffee

Although both contain caffeine, the experience differs. Coffee typically has more caffeine than black or green tea. However, tea contains L-theanine, an amino acid that promotes relaxation and counteracts caffeine jitters, leading to a smoother, sustained alertness. Coffee, without L-theanine, can cause a more intense high followed by a crash.


Feature	Coffee	Tea (Black)
Caffeine Content (per 250ml)	107–151 mg (brewed)	28–46 mg (brewed)
Presence of L-theanine	No	Yes
Effect on Alertness	Strong, potentially jittery boost followed by a crash	Gentle, sustained boost with a calming effect
Typical Dose Needed for Effects	Smaller quantity for potent effects	Larger quantity for comparable effects
Antioxidant Content	Yes, but varies by bean and roast	High, with antioxidants slowing caffeine absorption

Health Effects and Moderation

Moderate caffeine intake (up to 400 mg daily) is generally safe for healthy adults and may offer benefits like reduced disease risk. However, excessive intake can lead to anxiety, insomnia, and GI issues. Individual sensitivity varies based on genetics, size, and metabolism.

If dependency is suspected, gradually reducing intake is better than stopping abruptly to lessen withdrawal. Be aware of all caffeine sources, including energy drinks and chocolate. High caffeine intake risks are important for adolescents and pregnant women to understand, as they process it differently.

Conclusion

Caffeine is the addictive substance in tea and coffee, a common psychoactive stimulant. It works by blocking adenosine receptors, increasing alertness. While the experience differs between tea and coffee due to compounds like L-theanine in tea, the mechanism of dependence is similar. Tolerance and withdrawal indicate a mild physical dependence. For many, moderate consumption is acceptable, but for those dependent, understanding this science helps manage intake responsibly.

Authoritative research from the National Institutes of Health provides further insight into the biological basis of caffeine dependence.

Frequently Asked Questions

No, while caffeine creates a mild physical dependence with noticeable withdrawal symptoms, most scientists and medical professionals distinguish it from the severe, compulsive behaviors and neurological changes associated with addiction to drugs like cocaine or opioids.

Caffeine withdrawal symptoms usually start within 12 to 24 hours of cessation, peak between 20 to 51 hours, and can last from two to nine days, though this varies by individual.

Yes, on average, a cup of tea contains significantly less caffeine than a cup of brewed coffee. The exact amount depends on the type of tea or coffee bean and the preparation method.

Tea contains L-theanine, an amino acid that has calming properties and works with caffeine to provide a more gentle, prolonged alertness without the intense jitters or crash associated with coffee.

Overconsumption of caffeine can lead to symptoms such as anxiety, restlessness, insomnia, increased heart rate, and gastrointestinal irritation. A condition known as caffeinism can occur with high daily intake.

Adenosine is a natural neurotransmitter that promotes drowsiness by slowing down nerve cell activity. Caffeine is structurally similar to adenosine and blocks its receptors, which is how it keeps you feeling awake and alert.

To minimize withdrawal symptoms, it is recommended to gradually reduce your caffeine intake over several weeks instead of quitting abruptly. Staying hydrated with water and getting adequate sleep can also help.

Yes, moderate caffeine consumption has been associated with improved cognitive function, enhanced athletic performance, and a reduced risk of certain neurodegenerative diseases like Parkinson's.