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Tara S. Kerpelman and Dani Friedland/MEDILL

Two Medill reporters learn how to extract caffeine from tea in a chemistry lab at Northwestern University.

Reading between the leaves: Tea's benefits balanced by potential medical interactions

by Dani Friedland and Tara S. Kerpelman
March 10, 2009


Dani Friedland/MEDILL 

The size of the tea leaves used to steep tea impacts the levels of antioxidants in the tea. The tea in the tea bag is in small particles, which reduces the antioxidants. The loose leaf green tea (upper left) and blooming green and floral tea (lower left) would likely contain more antioxidants than the chai in the tea bag. The jasmine pearls (lower right) consist of two tea leaves wrapped around one bud.


Courtesy of Nikhil Roychowdhury/The Simple Leaf

Black, green, oolong and white teas are all made from the leaves of the same plant but are processed differently.


Dani Friedland/MEDILL

Data courtesy of the Tea Association of the United States of America


Dani Friedland/MEDILL

Chart based on a compilation of data from the USDA,, Lipton,,, and Chin JM, Merves ML, Goldberger BA, Sampson-Cone A, Cone EJ. "Caffeine content of brewed teas."  J. Anal. Toxicol. 2008 Octo; 32(8):702-4.

What do 127 million Americans have in common on any given day? They're drinking tea -- hot or iced, according to the Tea Association of the USA.

Some tea drinkers are choosing their beverage to absorb antioxidants and other health benefits associated with tea. But it's possible to have too much of a good thing, experts say.

Despite a healthy reputation, some chemical components in tea can interact with common medications such as aspirin.

One reason is that caffeine is in most teas. "It's potent stuff," said Dr. Stanley Segall, professor emeritus of nutrition and food science at Drexel University in Philadelphia. "You could properly classify caffeine as an addictive drug except the withdrawal symptoms are relatively innocuous."

Segall is also a food science communicator for the Institute of Food Technologists. He noted that such interactions should be common knowledge in the medical community. Much of what is known about tea interactions hinges on caffeine. "Caffeine is one of those things that's been looked at with suspicion for certainly the last 50 years," he said.

Black, green, oolong and white teas all come from the same plant: Camellia sinensis. Most teas consist of two leaves and a bud from the tea plant, which are then withered, rolled and exposed to the air to oxidize before being dried.

Oxygen absorbed from the air causes chemical changes within the leaves and possibly affects the level of antioxidants present in the plant, said Nikhil Roychowdhury, a tea wholesaler and owner of The Simple Leaf tea company in Chicago. 

"The jury is still out on this and it's an area of considerable research," Roychowdhury said.

There are four basic types of tea, Roychowdhury said. Black tea is oxidized the most and has the most concentrated flavors. Oolong tea, which is slightly lighter, is partially oxidized.

Green tea is fired quickly or pan-roasted to halt the natural oxidation process and help the leaves retain their green color. White tea is not oxidized and consists only of the bud, or in some cases, buds and leaves (depending on the type or style of white tea being made).

Less processed green and white teas have more antioxidants.

But any tea made with real tea leaves instead of herbs contains caffeine, which may interact with a variety of medications. Caffeine occurs naturally in tea, though most of it can be removed by commercial methods. 

The caffeine content in coffee "usually is three or more times higher," however, said Dr. Chun-Su Yuan, director of the Tang Center for Herbal Medicine Research at the University of Chicago.

"If you're on medications, beware. Caffeine can interfere," Segall said. Caffeine might interact with them because it has structural similarities to many drugs and chemically resembles hormones. For example, a hormonal interaction between caffeine and certain birth control medications reduces some women's ability to metabolize caffeine, Segall said. The result is that the caffeine stays in their systems and affects them longer. 

"[Caffeine] reacts with receptors in the brain called adenosine receptors and that actually gives you an energy boost," said Jim Coughlin, an independent food chemical safety consultant at Coughlin & Associates in California. Adenosine is a chemical in the body that carries messages between nerve cells in the brain. The caffeine binds to brain receptors, blocking their ability to bind to the adenosine that would otherwise give a calming, almost sleepy feeling, Coughlin said.

The interactions shouldn't be a problem for casual drinkers of tea and coffee, Segall said. "For the most part, the person who's drinking one or two cups in the morning [should not have] a problem."

It would take three or more cups of tea to reach a potentially problematic dose of caffeine because most Americans don't brew particularly strong tea.

By consuming five grams of tea leaves in tea anyone can get good antioxidant results, Yuan said. That's a little less than the weight of a Hershey's Kiss. The normal amount of tea leaves a person would consume is closer to two grams, about the weight of four Tic Tacs. Two grams may not contain enough antioxidants to obtain desirable effects. 

The powers of antioxidants are often highlighted among the reasons to drink tea. Antioxidants eat up free radicals,  very reactive cells in the body that can damage other cells. "If you have more antioxidants in the diet, they go to various organs and scavenge free radicals in the body," said Coughlin. He said the more antioxidants people take in, the more protection from disease you will get.

"Using teas would potentially reduce oxidative damage in the body,” said Yuan, who prefers loose leaf tea to packaged tea bags. "Tea leaves [are] better because [for] tea bags you usually grind the tea leaves into small particles," he said. "The antioxidant properties are reduced." Being aware of how you prepare your tea could help you maximize the amount of antioxidants you are taking in.

In some cases, caffeine actually strengthens the effect of a medication. Aspirin, for instance, is a common anticoagulant. Caffeine enhances the effects of aspirin, which in some cases can lead to concerns about internal bleeding.

Some people might try to avoid potential interactions by drinking herbal teas, most of which contain no caffeine, but Segall said some of them have interactions of their own. Chamomile, for instance, can interact with other chemicals and enhance the activity of aspirin. "A lot of the herbal teas contain substances called coumarines," Segall said. "They're related to blood thinners."

Large, complex molecules called tannins are also found in tea. "Tannins in tea reduce bioavailability of iron," said Coughlin. When you drink tea, iron binds to tannins and cannot be absorbed by your body, he said. "If it’s bound up in the tannin, a portion [of the iron] can go right through the body without it being digested."

Yuan said he isn't sure drinking tea will obviously cause these interactions, however. "It is possible but I didn't see very strong clinical study evidence for that," he said. "It depends on the concentration of the tea: If the tea is very strong, it possibly can have potential interactions with certain drugs." 

So what about Chicago's tea drinkers? Chicagoans leaving Argo Tea in downtown Chicago were unfamiliar with any potential interactions.

"I've never thought about that," said Rachel Cole, a 30-year-old librarian who comes to Argo four times a week for a mid-morning chai latté with soy milk. She doesn't think much about the health benefits, she said. But tea seems healthier to her than coffee.

The general consensus between tea shop owners, sellers and researchers is: There is no "best" tea for everyone. "This depends on the reasons a person has for drinking it," Yuan said. "If they want caffeine and they are 'addicted' to tea, then the stronger tea is better."

Tanya Govert, co-owner of Tea Essence tea shop on Milwaukee Avenue, said she prefers not to talk about the benefits of tea at all when people come into her shop. She said she focuses on helping tea drinkers find a tea they enjoy before taking health benefits into consideration. Most people won't continue to drink something they don't enjoy, she said.

Govert blends most of the store's teas based on flavor. For instance, a chai blend requires a strongly-flavored tea leaf because of the other flavors in the finished tea.

“My philosophy is that there are a lot of medical studies [on tea]," said Roychowdhury. "The FDA doesn’t allow health claims: For every study out there on tea, there’s another to contradict it.” 

“If it tastes good, drink it. There’s a high likelihood it is healthy,” he said.