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Guarana benefits and side effects

Guarana (Paullinia cupana) is a supplement taken for its stimulating effects.

The seeds of guarana —a fruit-bearing tree — have long been used in Amazonian medicine. They contain a range of stimulants, including caffeine, theophylline and theobromine. Guarana also contains such antioxidants as tannins, saponins and catechins (1).

Guarana is also being studied for its anti-cancer, neuroprotective, cardiovascular and anti-inflammatory effects.


Guarana may improve cognitive performance and mental fatigue. The results of a study published in the peer-reviewed journal Appetite, demonstrated guarana’s cognitive-enhancing properties. A group of 129 healthy participants (age 18-24) were given either a vitamin/mineral/guarana supplement or placebo drink.

Thirty minutes after drinking one of the two preparations, they completed 60 minutes of the Cognitive Demand Battery test.

The vitamin/mineral/guarana combination resulted in improved task performance, in terms of both increased speed and accuracy, compared to placebo. The supplement was also able to reduce the increase in mental fatigue associated with extended task performance (2).

More research is needed, as this study was confounded with the inclusion of other vitamins and minerals.

In another study, researchers assessed the effects of four different doses (37.5 mg, 75 mg, 150 mg and 300 mg) of a guarana extract on mood and cognitive effects throughout the day.

Guarana improved memory performance and increased alert and content mood ratings. Interestingly, the two lower doses produced more positive cognitive effects than the higher doses (3).

Guarana may improve heart health. According to an issue of the International Journal for Vitamin and Nutrition Research, extracts from the dried seeds of guarana have strong anti-platelet (blood clot preventing) activity.

It was determined that the catechins, epicatechins and caffeine present in the extracts might be responsible for this mechanism of action (4).

Another study showed the benefit of guarana in treating LDL and serum oxidation — events that increase one’s risk for developing atherosclerosis (clogged arteries).

Researchers used blood samples from 42 healthy elderly subjects who took guarana regularly or those who never took it. Those who consumed guarana demonstrated lower LDL oxidation than the other group.

It is believed that the total polyphenols are positively associated with lower LDL levels (5).

More human-based studies are needed, however, before recommendations can be made.

Guarana may help prevent metabolic syndrome. Metabolic syndrome is a group of conditions — high cholesterol or triglyceride levels, high blood pressure, excess body fat around the waist and high blood sugar — that can increase one’s risk for developing heart disease, stroke and diabetes (6).

A study was performed on a group of 637 elderly patients classified as either those who regularly drink guarana (group 1) or those who never drink guarana (group 2).

The prevalence of hypertension, obesity and metabolic syndrome in group 1 was lower than the prevalence found in the group 2. The males in group 1 had a lower waist circumference than the non-guarana drinking group. In addition, the females in group 1 had lower cholesterol (7).

Guarana may help reduce chemotherapy-related fatigue. Fatigue is often one of the most debilitating side effects of chemotherapy treatment. Researchers set out recently to evaluate the effectiveness of guarana extract on fatigue, sleep quality, anxiety and depression symptoms in a group of breast cancer chemotherapy patients.

Results show that the extract significantly improved scores in the Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F) questionnaire, the Functional Assessment of Chronic Illness Therapy-Endocrine Symptoms (FACT-ES) and the Brief Fatigue Inventory (BFI) global scores compared to placebo.

Guarana did not result in toxicities and did not worsen sleep quality or cause anxiety or depression (8).

When assessing the anti-fatigue effects of guarana in patients receiving radiation treatment, however, researchers found it to be not as effective (9).

Guarana may have anti-cancer properties. Early in vitro and animal studies show the potential cancer-killing effects of guarana extract, especially in colon cancer cells. The results of a study published in a 2016 issue of Anticancer Agents in Medicinal Chemistry, showed that all tested concentrations of the extract suppressed the growth of cancer cells and stimulated their death (10).

Another animal study showed that guarana treatment decreased the spread of cancer and increased the death of tumor cells. The focus of the study was melanoma lung metastases (11).

Guarana may play a role in treating depression. Using the forced swimming test on mice, researchers found that guarana supplementation significantly reduced the duration of immobility, suggesting an antidepressant-like effect (12).

A second study suggests that the crude extract of guarana seed produces an antidepressant-like effect after long-term administration in mice (13).

Guarana may protect against age-related eye conditions. In a study of elderly participants, it was noted that those who regularly consumed guarana self-reported having good vision, versus those who rarely or never consumed it.

In the same study, researchers performing an in vitro study found that guarana extract decreased oxidative damage in retinal cells. As a result, they are hopeful that it may improve age-related disorders such as macular degeneration (14).

Side effects

Guarana appears to be safe when taken in moderation. When taken in large doses, there have been reports of rapid heart rate, insomnia, headaches, seizures, nervousness, anxiety and upset stomach.

Those who are on anticoagulant or antiplatelet medication should avoid taking guarana.

Recommended dosage

Studies so far show that doses between 50–75 mg appear to provide health benefits. Further studies are needed to determine the optimal guarana dose.


Guarana is a supplement known for its stimulating properties due to its caffeine content. It has long been used in Amazonian medicine and has a range of stimulants in addition to caffeine, including theophylline and theobromine.

Guarana also contains such antioxidants as tannins, saponins and catechins which are being studied for their anti-cancer, neuroprotective, cardiovascular and anti-inflammatory effects.

Early studies show that guarana extract may play a role in improving cognitive performance, mental fatigue and heart health. It may also help prevent the spread of cancer cells and reduce chemotherapy-related fatigue.

There appears to be no notable side effects with moderate use. When taken in large doses, however, guarana may cause rapid heart rate, insomnia, headaches, nervousness, anxiety, stomach upset and even seizures.

Most of the published research so far comes from in vitro and animal studies. More studies and clinical trials are needed to evaluate the efficacy and safety in humans.

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Author: laura