Background

Oolong tea is made from the Camellia sinensis plant. Its dried leaves and leaf buds are used to make several different teas, including black and green teas.

Oolong tea is fermented for longer than green tea, but less than black tea. It contains caffeine which affects thinking and alertness. Caffeine works by stimulating the central nervous system, heart, and muscles.

People use oolong tea for mental alertness. It is also used for obesity, diabetes, high blood pressure, autism, and many other conditions, but there is no good scientific evidence to support these other uses.

Don't confuse oolong tea with other caffeine sources, including coffee, black tea, and green tea. These are not the same.

Safety Safety definitions

When taken by mouth: Oolong tea is commonly consumed as a beverage. Drinking oolong tea in moderate amounts (about 4 cups daily) is likely safe for most people.

Drinking more than 4 cups of oolong tea daily is possibly unsafe. Drinking large amounts might cause side effects due to the caffeine content. These side effects can range from mild to serious and include headache and irregular heartbeat.

Special Precautions & Warnings:

Pregnancy: Drinking moderate amounts of oolong tea during pregnancy is possibly safe. Do not drink more than 3 cups of oolong tea daily. This provides about 300 mg of caffeine. Consuming more than this during pregnancy is possibly unsafe and has been linked to an increased risk of miscarriage, increased risk of sudden infant death syndrome (SIDS), and other negative effects, including symptoms of caffeine withdrawal in newborns and lower birth weight.

Breast-feeding: Drinking moderate amounts of oolong tea while breast-feeding is possibly safe. But drinking more than 3 cups of oolong tea daily is possibly unsafe. The caffeine in oolong tea is passed into breastmilk. It might cause irritability and increased bowel movements in nursing infants.

Children: Oolong tea is possibly safe in children when consumed in amounts found in food and beverages.

Anxiety disorders: The caffeine in oolong tea might make anxiety disorders worse.

Bleeding disorders: Oolong tea contains caffeine. Caffeine might slow blood clotting. Use caffeine cautiously if you have a bleeding disorder.

Heart problems: Oolong tea contains caffeine. Caffeine can cause irregular heartbeat in certain people. If you have a heart condition, use caffeine with caution.

Diabetes: Oolong tea contains caffeine. Caffeine might affect blood sugar levels. Use caffeine with caution if you have diabetes.

Diarrhea: Oolong tea contains caffeine. Caffeine, especially when taken in large amounts, can worsen diarrhea.

Seizures: Oolong tea contains caffeine. High doses of caffeine might cause seizures or decrease the effects of drugs used to prevent seizures. If you have ever had a seizure, don't use high doses of caffeine or caffeine-containing products such as oolong tea.

Glaucoma: Oolong tea contains caffeine. Caffeine can increase the pressure inside the eye. The increase occurs within 30 minutes and lasts for at least 90 minutes.

High blood pressure: Oolong tea contains caffeine. Caffeine might increase blood pressure. But this doesn't seem to happen in people who regularly drink oolong tea or other caffeinated products.

Irritable bowel syndrome (IBS): Oolong tea contains caffeine. The caffeine in oolong tea, especially when taken in large amounts, can worsen diarrhea and might worsen symptoms of IBS.

Brittle bones (osteoporosis): Drinking oolong tea can increase the amount of calcium that is flushed out in the urine. This might weaken bones. If you have osteoporosis, don't drink more than 3 cups of oolong tea daily. If you are generally healthy and get enough calcium from your food or supplements, drinking about 4 cups of oolong tea daily doesn't seem to increase the risk of getting osteoporosis.

Effectiveness

Dosing & administration

Oolong tea is commonly consumed by adults as a beverage, typically in amounts of 1-4 cups daily. Speak with a healthcare provider to find out what dose might be best for a specific condition.

Interactions with pharmaceuticals

Adenosine (Adenocard)

Interaction Rating=Moderate Be cautious with this combination.

Oolong tea contains caffeine. The caffeine in oolong tea might block the effects of adenosine, which is used to do a test called a cardiac stress test. Stop consuming oolong tea or other caffeine-containing products at least 24 hours before a cardiac stress test.

Alcohol (Ethanol)

Interaction Rating=Minor Be watchful with this combination.

Oolong tea contains caffeine. The body breaks down the caffeine in oolong tea to get rid of it. Alcohol can decrease how quickly the body breaks down caffeine. Taking oolong tea along with alcohol might increase the risk for side effects from caffeine, including jitteriness, headache, and fast heartbeat.

Antibiotics (Quinolone antibiotics)

Interaction Rating=Minor Be watchful with this combination.

Oolong tea contains caffeine. The body breaks down caffeine to get rid of it. Some antibiotics might decrease how quickly the body breaks down caffeine. Taking these antibiotics along with oolong tea can increase the risk for side effects from caffeine, such as jitteriness, headache, and fast heartbeat.

Birth control pills (Contraceptive drugs)

Interaction Rating=Minor Be watchful with this combination.

Oolong tea contains caffeine. The body breaks down caffeine to get rid of it. Birth control pills can decrease how quickly the body breaks down caffeine. This might increase the risk for side effects from caffeine, such as jitteriness, headache, and fast heartbeat.

Cimetidine (Tagamet)

Interaction Rating=Moderate Be cautious with this combination.

Oolong tea contains caffeine. The body breaks down caffeine to get rid of it. Cimetidine can decrease how quickly the body breaks down caffeine. Taking cimetidine along with oolong tea might increase the risk of side effects from caffeine, such as jitteriness, headache, and fast heartbeat.

Clozapine (Clozaril)

Interaction Rating=Moderate Be cautious with this combination.

The body breaks down clozapine to get rid of it. The caffeine in oolong tea seems to decrease how quickly the body breaks down clozapine. Taking oolong tea along with clozapine can increase the effects and side effects of clozapine.

Dipyridamole (Persantine)

Interaction Rating=Moderate Be cautious with this combination.

Oolong tea contains caffeine. The caffeine in oolong tea might block the effects of dipyridamole. Dipyridamole is often used by doctors to do a test on the heart called a cardiac stress test. Stop consuming oolong tea or other caffeine-containing products at least 24 hours before a cardiac stress test.

Disulfiram (Antabuse)

Interaction Rating=Moderate Be cautious with this combination.

Oolong tea contains caffeine. The body breaks down caffeine to get rid of it. Disulfiram can decrease how quickly the body gets rid of caffeine. Taking oolong tea along with disulfiram might increase the risk of side effects from caffeine, such as jitteriness, headache, and fast heartbeat.

Ephedrine

Interaction Rating=Major Do not take this combination.

Oolong tea contains caffeine. Caffeine is a stimulant drug. Stimulant drugs speed up the nervous system. Ephedrine is also a stimulant drug. Taking oolong tea along with ephedrine might cause too much stimulation and sometimes serious side effects and heart problems.

Estrogens

Interaction Rating=Moderate Be cautious with this combination.

Oolong tea contains caffeine. The body breaks down caffeine to get rid of it. Estrogens can decrease how quickly the body breaks down caffeine. Taking estrogen and drinking oolong tea can increase the risk of side effects from caffeine, such as jitteriness, headache, and fast heartbeat.

Fluconazole (Diflucan)

Interaction Rating=Minor Be watchful with this combination.

Oolong tea contains caffeine. The body breaks down caffeine to get rid of it. Fluconazole might decrease how quickly the body gets rid of caffeine. Taking oolong tea along with fluconazole might increase the risk of side effects from caffeine, such as jitteriness, headache, and fast heartbeat.

Flutamide (Eulexin)

Interaction Rating=Moderate Be cautious with this combination.

The body breaks down flutamide to get rid of it. The caffeine in oolong tea might decrease how quickly the body gets rid of flutamide. This could increase the effects and side effects of flutamide.

Fluvoxamine (Luvox)

Interaction Rating=Moderate Be cautious with this combination.

Oolong tea contains caffeine. The body breaks down caffeine to get rid of it. Fluvoxamine can decrease how quickly the body breaks down caffeine. Taking oolong tea along with fluvoxamine might increase the risk of side effects from caffeine, such as jitteriness, headache, and fast heartbeat.

Lithium

Interaction Rating=Moderate Be cautious with this combination.

The caffeine in oolong tea can increase how quickly the body gets rid of lithium. If you take products that contain caffeine and you also take lithium, do not stop taking caffeine all at once. Stopping caffeine too quickly can increase the side effects of lithium.

Medications for asthma (Beta-adrenergic agonists)

Interaction Rating=Moderate Be cautious with this combination.

Oolong tea contains caffeine. Caffeine can stimulate the heart. Some medications for asthma can also stimulate the heart. Taking caffeine with some medications for asthma might cause too much stimulation and cause heart problems.

Medications for depression (MAOIs)

Interaction Rating=Moderate Be cautious with this combination.

Oolong tea contains caffeine. There is some concern that caffeine can interact with certain medications, called MAOIs. If caffeine is taken with these medications, it might increase the risk for serious side effects including fast heartbeat and very high blood pressure.

Some common MAOIs include phenelzine (Nardil), selegiline (Zelapar), and tranylcypromine (Parnate).

Medications for diabetes (Antidiabetes drugs)

Interaction Rating=Minor Be watchful with this combination.

Oolong tea contains caffeine. Caffeine can either increase or decrease blood sugar. Diabetes medications are used to lower blood sugar. Taking some medications for diabetes along with caffeine might change the effects of the diabetes medications. Monitor your blood sugar closely. The dose of your diabetes medication might need to be changed.

Medications that slow blood clotting (Anticoagulant / Antiplatelet drugs)

Interaction Rating=Moderate Be cautious with this combination.

Oolong tea might slow blood clotting. Taking oolong tea along with medications that also slow blood clotting might increase the risk of bruising and bleeding.

Methoxsalen (Oxsoralen)

Interaction Rating=Minor Be watchful with this combination.

Oolong tea contains caffeine. Methoxsalen can decrease how quickly the body breaks down caffeine. Taking caffeine along with methoxsalen might increase the risk of side effects from caffeine such as jitteriness, headache, and fast heartbeat.

Mexiletine (Mexitil)

Interaction Rating=Minor Be watchful with this combination.

Oolong tea contains caffeine. The body breaks down caffeine to get rid of it. Mexiletine can decrease how quickly the body breaks down caffeine. Taking mexiletine along with oolong tea might increase the risk of side effects from caffeine, such as jitteriness, headache, and fast heartbeat.

Nicotine

Interaction Rating=Moderate Be cautious with this combination.

Oolong tea contains caffeine. Caffeine can stimulate the heart. Nicotine can also stimulate the heart. Taking oolong tea with nicotine might cause too much stimulation and cause heart problems, such as increased heart rate or blood pressure.

Pentobarbital (Nembutal)

Interaction Rating=Moderate Be cautious with this combination.

Oolong tea contains caffeine. The stimulant effects of caffeine can block the sleep-producing effects of pentobarbital.

Phenobarbital (Luminal)

Interaction Rating=Moderate Be cautious with this combination.

Phenobarbital is a drug used to treat seizures. The caffeine in oolong tea might decrease the effects of phenobarbital. This might increase the risk of seizures in some people.

Phenothiazines

Interaction Rating=Minor Be watchful with this combination.

Oolong tea contains caffeine. Phenothiazines can decrease how quickly the body breaks down caffeine. Taking phenothiazines along with caffeine might increase the effects and side effects of caffeine.

Phenylpropanolamine

Interaction Rating=Moderate Be cautious with this combination.

The caffeine in oolong tea can stimulate the body. Phenylpropanolamine can also stimulate the body. Taking caffeine along with phenylpropanolamine might cause too much stimulation and increase the risk of a fast heartbeat, high blood pressure, and nervousness.

Phenytoin (Dilantin)

Interaction Rating=Moderate Be cautious with this combination.

Phenytoin is a drug used to treat seizures. The caffeine in oolong tea can decrease the effects of phenytoin. Taking oolong tea with phenytoin might decrease the effects of phenytoin and increase the risk of seizures in some people.

Riluzole (Rilutek)

Interaction Rating=Moderate Be cautious with this combination.

Drinking oolong tea might decrease how quickly the body breaks down riluzole. This might increase the effects and side effects of riluzole.

Stimulant drugs

Interaction Rating=Moderate Be cautious with this combination.

Stimulants, such as amphetamines and cocaine, speed up the nervous system. By speeding up the nervous system, stimulant medications can increase blood pressure and speed up the heartbeat. Oolong tea contains caffeine. Caffeine can also speed up the nervous system. Taking oolong tea along with stimulant drugs might cause serious problems including increased heart rate and high blood pressure.

Terbinafine (Lamisil)

Interaction Rating=Minor Be watchful with this combination.

Oolong tea contains caffeine. Terbinafine can decrease how quickly the body gets rid of caffeine. Taking terbinafine with oolong tea might increase the risk of side effects from caffeine, such as jitteriness, headache, and fast heartbeat.

Theophylline

Interaction Rating=Moderate Be cautious with this combination.

Oolong tea contains caffeine. Caffeine works similarly to theophylline. Caffeine can also decrease how quickly the body gets rid of theophylline. This might increase the effects and side effects of theophylline.

Tiagabine (Gabitril)

Interaction Rating=Minor Be watchful with this combination.

Oolong tea contains caffeine. Taking caffeine over a long time period along with tiagabine can increase the amount of tiagabine in the body. This might increase the effects and side effects of tiagabine.

Ticlopidine (Ticlid)

Interaction Rating=Minor Be watchful with this combination.

Oolong tea contains caffeine. Ticlopidine can decrease how quickly the body gets rid of caffeine. Taking caffeine along with ticlopidine might increase the risk of side effects from caffeine, including jitteriness, headache, and fast heartbeat.

Valproate

Interaction Rating=Moderate Be cautious with this combination.

Valproate is a drug used to treat seizures. The caffeine in oolong tea might decrease the effects of valproate and increase the risk of seizures in some people.

Verapamil (Calan, others)

Interaction Rating=Moderate Be cautious with this combination.

Oolong tea contains caffeine. Verapamil can decrease how quickly the body gets rid of caffeine. Taking caffeine along with verapamil can increase the risk of caffeine side effects including jitteriness, headache, and fast heartbeat.

Water pills (Diuretic drugs)

Interaction Rating=Moderate Be cautious with this combination.

Oolong tea contains caffeine. Caffeine, especially in large amounts, can reduce potassium levels in the body. "Water pills" can also decrease potassium levels in the body. Taking large amounts of caffeine along with "water pills" might decrease potassium levels too much.

Interactions with herbs & supplements

Bitter orange: Oolong tea contains caffeine. Using bitter orange along with products that contain caffeine can increase blood pressure and heart rate in otherwise healthy adults with normal blood pressure. This could increase the risk of serious heart problems.
Caffeine-containing herbs and supplements: Oolong tea contains caffeine. Taking it along with other supplements that contain caffeine might increase caffeine side effects. Examples of supplements that contain caffeine include black tea, coffee, green tea, guarana, and yerba mate.
Calcium: High caffeine intake from foods and beverages, including oolong tea, can increase the amount of calcium that is flushed out of the body in the urine.
Cordyceps: Oolong tea contains caffeine. The body breaks down caffeine to get rid of it. Cordyceps might increase how quickly the body gets rid of caffeine. This might decrease the effects of caffeine.
Creatine: Combining caffeine, ephedra, and creatine might increase the risk of serious unwanted side effects. One athlete who used this combination, as well as some other supplements to improve performance, suffered a stroke. Researchers worry the stroke might have been caused by the supplements.
Danshen: Oolong tea contains caffeine. The body breaks down caffeine to get rid of it. Danshen can decrease how quickly the body gets rid of caffeine. Drinking oolong tea and taking danshen might increase the risk of side effects from caffeine, such as jitteriness, headache, and fast heartbeat.
Echinacea: Oolong tea contains caffeine. The body breaks down caffeine to get rid of it. Echinacea can decrease how quickly the body gets rid of caffeine. Drinking oolong tea and taking echinacea might increase the risk of side effects from caffeine, including jitteriness, headache, and fast heartbeat.
Ephedra: Oolong tea contains caffeine. Using ephedra with caffeine might increase the risk of serious life-threatening or disabling conditions such as hypertension, heart attack, stroke, seizures, and death. Avoid this combination.
Folic acid: Oolong tea might reduce the amount of folate that the body can absorb and use, especially in pregnant females.
Genistein-containing herbs and supplements: Oolong tea contains caffeine. A chemical called genistein can decrease how quickly the body gets rid of caffeine. Drinking oolong tea and taking genistein might increase the risk of side effects from caffeine, including jitteriness, headache, and an increased heartbeat. Examples of supplements that contain genistein include cumin, dyer's broom, kudzu, red clover, and soy.
Herbs and supplements that might slow blood clotting: Oolong tea might slow blood clotting and increase the risk of bleeding. Taking it with other supplements with similar effects might increase the risk of bleeding in some people. Examples of supplements with this effect include garlic, ginger, ginkgo, nattokinase, and Panax ginseng.
Iron: Oolong tea might interfere with the body's ability to absorb iron. This probably isn't a problem for most people. If you are iron-deficient, drink tea between meals rather than with meals to reduce this concern.
Kudzu: Oolong tea contains caffeine. The body breaks down caffeine to get rid of it. Kudzu can decrease how quickly the body gets rid of caffeine. Drinking oolong tea and taking kudzu might increase the risk of side effects from caffeine, such as jitteriness, headache, and fast heartbeat.
Magnesium: Drinking large amounts of oolong tea can increase the amount of magnesium that is flushed out in the urine.
Melatonin: Oolong tea contains caffeine. Taking caffeine and melatonin together can increase melatonin levels. Caffeine can also increase natural melatonin levels in healthy individuals.

Interactions with foods

Oolong tea appears to reduce absorption of iron from foods. Drinking oolong tea in between meals rather than with meals should reduce this concern.

Adding milk to oolong tea appears to reduce some of the heart health benefits of drinking tea. Milk might bind with the antioxidants in tea and keep them from being absorbed. But it's not clear if this is a real concern.