Background

Guarana (Paullinia cupana) is a plant native to the Amazon. It is a common ingredient of energy drinks and can be unsafe in large amounts.

Guarana contains caffeine. Caffeine works by stimulating the central nervous system, heart, and muscles. Guarana also contains theophylline and theobromine, which are chemicals similar to caffeine.

People take guarana by mouth for obesity, athletic performance, mental performance, to increase energy, and for many other reasons, but there is no good scientific evidence to support these uses. Guarana can also be unsafe when taken long-term in large amounts.

Safety Safety definitions

When taken by mouth: Guarana is likely safe for most adults when taken in amounts commonly found in foods. Guarana is possibly safe when taken as medicine, short-term.

When taken in high doses for a long time, guarana is possibly unsafe. Guarana contains caffeine. Doses containing more than 400 mg of caffeine daily have been linked to side effects. Side effects depend on the dose. At typical doses, the caffeine in guarana can cause insomnia, nervousness, stomach irritation, vomiting, and many other side effects.

Special Precautions & Warnings:

Pregnancy: Guarana is possibly safe during pregnancy when taken in amounts commonly found in foods. If you are pregnant, guarana should be taken with caution due to the caffeine content. Small amounts are probably not harmful. However, taking guarana in high doses by mouth is possibly unsafe. Consuming more than 300 mg of caffeine daily has been linked to an increased risk of miscarriage and other negative effects.

Breast-feeding: Caffeine passes into breast milk and can affect a nursing infant. If you are nursing, closely monitor caffeine intake to make sure it is on the low side. High intake of caffeine can cause sleep problems, irritability, and increased bowel activity in breastfed infants.

Anxiety: The caffeine in guarana might make feelings of anxiety worse.

Bladder control problems: Guarana contains caffeine. The caffeine in guarana might reduce bladder control, especially in older adults. If you need to urinate often with high urgency, use guarana cautiously.

Bleeding disorders: There is some concern that the caffeine in guarana might make bleeding disorders worse. If you have a bleeding disorder, check with your healthcare provider before starting guarana.

Diabetes: Guarana contains caffeine. Some research suggests that caffeine may affect the way the body uses sugar and might worsen diabetes. If you have diabetes, use guarana with caution and monitor your blood sugar closely.

Diarrhea. Guarana contains caffeine. The caffeine in guarana, especially when taken in large amounts, can worsen diarrhea.

Glaucoma. The caffeine in guarana increases the pressure inside the eye. The increase occurs within 30 minutes and lasts for at least 90 minutes after drinking caffeinated beverages.

Heart disease: The caffeine in guarana might cause irregular heartbeat in certain people. Use with caution.

High blood pressure: Guarana contains caffeine. The caffeine in guarana might raise blood pressure. However, this effect might be less in people who consume caffeine regularly.

Irritable bowel syndrome (IBS): Guarana contains caffeine. The caffeine in guarana, especially when taken in large amounts, can worsen diarrhea and might make diarrhea from IBS worse.

Seizures. Guarana contains caffeine. There is a concern that high doses of caffeine might cause seizures or decrease the effects of drugs used to prevent seizures. If you have seizures, talk to your healthcare provider before using guarana.

Weak bones (Osteoporosis): The caffeine in guarana can flush calcium out of the body through the kidneys. This calcium loss might weaken bones. If you have osteoporosis, don't consume more than 300 mg of caffeine per day. Taking calcium supplements may also help to replace any lost calcium. If you are generally healthy and getting enough calcium from your food or supplements, taking up to 400 mg of caffeine per day doesn't seem to increase the risk of getting osteoporosis.

Effectiveness

Dosing & administration

Guarana has most often been used by adults in doses of 75-100 mg by mouth daily for up to 4 weeks. 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.

Guarana contains caffeine. The caffeine in guarana might block the affects of adenosine, which is often used by doctors to do a test called a cardiac stress test. Stop consuming guarana at least 24 hours before a cardiac stress test.

Alcohol (Ethanol)

Interaction Rating=Minor Be watchful with this combination.

The body breaks down the caffeine in guarana to get rid of it. Alcohol can decrease how quickly the body breaks down caffeine. Taking guarana along with alcohol might increase the risk for caffeine side effects, such as jitteriness, headache, and fast heartbeat.

Antibiotics (Quinolone antibiotics)

Interaction Rating=Minor Be watchful with this combination.

The body breaks down caffeine from guarana to get rid of it. Some drugs can decrease how quickly the body breaks down caffeine. Taking these drugs along with guarana might increase the risk of caffeine side effects including jitteriness, headache, and fast heartbeat.

Birth control pills (Contraceptive drugs)

Interaction Rating=Minor Be watchful with this combination.

Guarana 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 caffeine side effects, such as jitteriness, headache, and fast heartbeat.

Carbamazepine (Tegretol)

Interaction Rating=Moderate Be cautious with this combination.

Carbamazepine is used to treat seizures. The caffeine in guarana might reduce the effects of carbamazepine. In theory, taking guarana with carbamazepine might reduce its effects and increase the risk of seizures in some people.

Cimetidine (Tagamet)

Interaction Rating=Moderate Be cautious with this combination.

Guarana contains caffeine. The body breaks down caffeine to get rid of it. Cimetidine can decrease how quickly your body breaks down caffeine. Taking cimetidine along with guarana might increase the chance of caffeine side effects including 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 guarana seems to decrease how quickly the body breaks down clozapine. Taking guarana along with clozapine can increase the effects and side effects of clozapine.

Dipyridamole (Persantine)

Interaction Rating=Moderate Be cautious with this combination.

Guarana contains caffeine. The caffeine in guarana might block the effects of dipyridamole, which is often used by doctors to do a test called a cardiac stress test. Stop consuming guarana at least 24 hours before a cardiac stress test.

Disulfiram (Antabuse)

Interaction Rating=Moderate Be cautious with this combination.

Guarana contains caffeine. The body breaks down caffeine to get rid of it. Disulfiram can decrease how quickly the body gets rid of caffeine. Taking guarana along with disulfiram might increase the chance of caffeine side effects, including jitteriness, headache, and fast heartbeat.

Ephedrine

Interaction Rating=Major Do not take this combination.

Stimulant drugs speed up the nervous system. Caffeine (contained in guarana) and ephedrine are both stimulant drugs. Taking guarana along with ephedrine might cause too much stimulation and serious side effects and heart problems.

Estrogens

Interaction Rating=Moderate Be cautious with this combination.

Guarana contains caffeine. The body breaks down the caffeine to get rid of it. Estrogens can decrease how quickly the body breaks down caffeine. Taking guarana along with estrogens can increase the risk of caffeine side effects, including jitteriness, headache, and fast heartbeat.

Ethosuximide

Interaction Rating=Moderate Be cautious with this combination.

Ethosuximide is used to treat seizures. Caffeine in guarana might reduce the effects of ethosuximide. In theory, taking guarana with ethosuximide might reduce its effects and increase the risk of seizures in some people.

Felbamate

Interaction Rating=Moderate Be cautious with this combination.

Felbamate is used to treat seizures. Caffeine in guarana might reduce the effects of felbamate. In theory, taking guarana with felbamate might reduce its effects and increase the risk of seizures.

Fluconazole (Diflucan)

Interaction Rating=Minor Be watchful with this combination.

Guarana contains caffeine. The body breaks down caffeine to get rid of it. Fluconazole might decrease how quickly the body gets rid of caffeine. Taking guarana along with fluconazole might increase the risk of caffeine side effects 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. Caffeine in guarana might decrease how quickly the body breaks down flutamide. In theory, taking guarana along with flutamide might increase the effects and side effects of flutamide.

Fluvoxamine (Luvox)

Interaction Rating=Moderate Be cautious with this combination.

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

Lithium

Interaction Rating=Moderate Be cautious with this combination.

The body naturally gets rid of lithium. The caffeine in guarana can increase how quickly the body gets rid of lithium. If you take products that contain caffeine and you take lithium, don't change your dose of caffeine quickly. Stopping caffeine too quickly can increase the side effects of lithium. If you stop using caffeine, reduce the dose slowly.

Medications for asthma (Beta-adrenergic agonists)

Interaction Rating=Moderate Be cautious with this combination.

Guarana 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 heart problems.

Medications for depression (MAOIs)

Interaction Rating=Moderate Be cautious with this combination.

Guarana 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.

Medications for diabetes (Antidiabetes drugs)

Interaction Rating=Minor Be watchful with this combination.

Guarana might lower blood sugar levels. Taking guarana along with diabetes medications might cause blood sugar to drop too low. Monitor your blood sugar closely.

Medications that decrease the breakdown of other medications by the liver (Cytochrome P450 1A2 (CYP1A2) inhibitors)

Interaction Rating=Minor Be watchful with this combination.

Guarana is changed and broken down by the liver. Some drugs decrease how quickly the liver changes and breaks down guarana. This could change the effects and side effects of guarana.

Medications that slow blood clotting (Anticoagulant / Antiplatelet drugs)

Interaction Rating=Moderate Be cautious with this combination.

Guarana might slow blood clotting. Taking guarana along with medications that also slow blood clotting might increase the risk of bruising and bleeding.

Metformin (Glucophage)

Interaction Rating=Minor Be watchful with this combination.

Guarana contains caffeine. The body breaks down caffeine to get rid of it. Metformin can decrease how quickly the body breaks down caffeine. Taking metformin along with guarana might increase the risk of caffeine side effects. such as jitteriness, headache, and fast heartbeat.

Methoxsalen (Oxsoralen)

Interaction Rating=Minor Be watchful with this combination.

Guarana contains caffeine. The body breaks down caffeine to get rid of it. Methoxsalen can decrease how quickly the body breaks down caffeine. Taking methoxsalen along with guarana might increase the risk of caffeine side effects, such as jitteriness, headache, and fast heartbeat.

Mexiletine (Mexitil)

Interaction Rating=Minor Be watchful with this combination.

Guarana 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 guarana might increase the risk of caffeine side effects, such as jitteriness, headache, and fast heartbeat.

Nicotine

Interaction Rating=Moderate Be cautious with this combination.

Stimulant drugs such as nicotine speed up the nervous system. The caffeine in guarana might also speed up the nervous system. Taking guarana along with stimulant drugs might cause serious problems including increased heart rate and high blood pressure.

Pentobarbital (Nembutal)

Interaction Rating=Moderate Be cautious with this combination.

The stimulant effects of the caffeine in guarana can block the sleep-producing effects of pentobarbital.

Phenobarbital (Luminal)

Interaction Rating=Moderate Be cautious with this combination.

Phenobarbital is used to treat seizures. Caffeine, in guarana might reduce the effects of phenobarbital. In theory, taking guarana with phenobarbital might reduce its effects and increase the risk of seizures.

Phenothiazines

Interaction Rating=Minor Be watchful with this combination.

Guarana contains caffeine. The body breaks down caffeine to get rid of it. Phenothiazines can decrease how quickly the body breaks down caffeine. Taking phenothiazines along with guarana might increase the risk of caffeine side effects, such as jitteriness, headache, and fast heartbeat.

Phenylpropanolamine

Interaction Rating=Moderate Be cautious with this combination.

The caffeine in guarana can stimulate the body. Phenylpropanolamine can also stimulate the body. Taking guarana along with phenylpropanolamine might cause too much stimulation and increase heartbeat, blood pressure, and cause nervousness.

Phenytoin (Dilantin)

Interaction Rating=Moderate Be cautious with this combination.

Phenytoin is used to control some types of seizures. Caffeine in guarana might reduce the effects of phenytoin. In theory, taking guarana with phenytoin might reduce its effects and increase the risk of seizures.

Pioglitazone (Actos)

Interaction Rating=Moderate Be cautious with this combination.

The caffeine in guarana might increase the amount of pioglitazone that the body absorbs. Taking guarana might increase the effects and adverse effects of pioglitazone.

Riluzole (Rilutek)

Interaction Rating=Moderate Be cautious with this combination.

The body breaks down riluzole to get rid of it. Taking guarana can decrease how fast the body breaks down riluzole and 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. Caffeine in guarana can also speed up the nervous system. Taking guarana 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.

Guarana contains caffeine. The body breaks down caffeine to get rid of it. Terbinafine can decrease how fast the body gets rid of caffeine and increase the risk of caffeine side effects such as jitteriness, headache, and fast heartbeat.

Theophylline

Interaction Rating=Moderate Be cautious with this combination.

Guarana contains caffeine. Caffeine works similarly to theophylline. Caffeine can also decrease how quickly the body gets rid of theophylline. Taking guarana along with theophylline might increase the effects and side effects of theophylline.

Tiagabine (Gabitril)

Interaction Rating=Minor Be watchful with this combination.

Tiagabine is used to treat seizures. There is some concern that caffeine can reduce the effects of tiagabine. But studies show that tiagabine still works even when taken with caffeine.

Ticlopidine (Ticlid)

Interaction Rating=Minor Be watchful with this combination.

Guarana contains caffeine. The body breaks down caffeine to get rid of it. Ticlopidine can decrease how fast the body gets rid of caffeine. In theory, taking guarana along with ticlopidine might increase the risk of caffeine side effects, such as jitteriness, headache, and fast heartbeat.

Valproate

Interaction Rating=Moderate Be cautious with this combination.

Valproate is used to treat seizures. Caffeine in guarana might reduce the effects of valproate. In theory, taking guarana with valproate might reduce its effects and increase the risk of seizures.

Verapamil (Calan, others)

Interaction Rating=Moderate Be cautious with this combination.

The body breaks down the caffeine in guarana to get rid of it. Verapamil can decrease how quickly the body gets rid of caffeine. Taking guarana 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.

Guarana contains caffeine. Caffeine can decrease potassium levels. "Water pills" can also decrease potassium levels. Taking guarana along with "water pills" might make potassium levels drop too low.

Interactions with herbs & supplements

Bitter orange: Guarana contains caffeine. Taking bitter orange along with herbs that contain caffeine, such as guarana, can increase blood pressure and heart rate in people who otherwise have normal blood pressure. This might increase the chance of developing problems with the heart and blood vessels.
Caffeine-containing herbs and supplements: Guarana 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, and yerba mate.
Calcium: High caffeine intake from foods, beverages, and herbs including guarana increases how much calcium the body loses in the urine. This might lower calcium levels.
Creatine: There is some concern that taking caffeine with creatine might reduce the beneficial effects that creatine has on athletic performance.
Danshen: Guarana contains caffeine. The body breaks down caffeine to get rid of it. Danshen might decrease how quickly the body breaks down caffeine. Using danshen with guarana might increase the risk of caffeine side effects.
Echinachea: Guarana contains caffeine. The body breaks down caffeine to get rid of it. Echinacea might decrease how quickly the body breaks down caffeine. Using echinacea with guarana might increase the risk of caffeine side effects.
Ephedra: Stimulants speed up the nervous system. Caffeine (contained in guarana) and ephedra are both stimulants. Taking guarana along with ephedra might cause too much stimulation and serious side effects and heart problems.
Genistein-containing herbs and supplements: Guarana contains genistein. Genistein might decrease how quickly the body breaks down caffeine. Taking guarana with caffeine might increase caffeine levels and side effects. Examples of supplements that contain genistein include cumin, dyer's broom, kudzu, red clover, and soy.
Herbs and supplements that might slow blood clotting: Guarana 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.
Kudzu: Guarana contains caffeine. The body breaks down caffeine to get rid of it. Kudzu might decrease how quickly the body breaks down caffeine. Using kudzu with guarana might increase the risk of caffeine side effects.
Magnesium: High caffeine intake from foods, beverages, and herbs including guarana increases how much magnesium the body loses in the urine. This might lower magnesium levels.
Melatonin: Guarana contains caffeine. Taking caffeine along with melatonin can increase melatonin levels. In theory, taking guarana with melatonin might increase melatonin effects and side effects.

Interactions with foods

There are no known interactions with foods.