Guarana: Adverse Reactions. Interactions. Pregnancy Use. Practice Points


Animal tests have shown that high doses of 1000-2000 mg/kg (intraperitoneal and oral) do not induce significant alterations in parameters for toxicological screening, suggesting an absence of toxicity.

Adverse Reactions

Due to a lack of clinical studies testing guarana as a stand-alone treatment, it is difficult to determine what adverse reactions may exist.

Based on caffeine content, the following adverse effects may theoretically occur at high doses: agitation, tremor, anxiety, restlessness, headache, seizures, tachycardia and premature ventricular contractions, diarrhea, gastrointestinal cramping, nausea and vomiting and diuresis.

Significant Interactions

Controlled studies are not available, therefore interactions are theoretical and based on evidence of pharmacological activity with uncertain clinical significance.


Additive stimulant activity is theoretically possible — use with caution.


Antagonistic effects are theoretically possible due to the herb’s CNS stimulant activity. However, one in vivo study found no interaction with pentobarbital. Observe patients taking this combination.


Additive diuresis effects are theoretically possible — use this combination with caution.


Increased bleeding is theoretically possible as in vitro and in vivo research has identified antiplatelet activity for guarana — use this combination with caution.


Antagonist effects theoretically possible — use caution.


Additive effects are theoretically possible as in vitro and in vivo research has identified antiplatelet activity for guarana — observe patients taking this combination.


Long-term use of high-dose supplements can result in reduced potassium levels, which lowers the threshold for drug toxicity. Avoid long-term use of high-dose guarana preparations.


The inhibitory effect of caffeine on CYP1A2 may cause other interactions, but this is highly speculative for guarana.

Contraindications and Precautions

Caffeine is no longer a prohibited substance under the Olympic Games antidoping code.

Refer to the following website for further information —

Contraindicated in hypertension and cardiac arrhythmias.

Use with caution in anxiety states, hypertension, diabetes, gastric ulcers and chronic headache.

Suspend use of concentrated extracts 1 week before major surgery.

Pregnancy Use

The use of caffeine-containing preparations should be limited during pregnancy; therefore, the caffeine content of guarana products should be checked before use.

Practice Points / Patient Counselling

• Guarana has mild CNS stimulant properties and may increase alertness, cognitive function and possibly mood.

• Current evidence is inconclusive as to whether guarana also enhances physical stamina.

• It has been used in combination with other herbs as a weight-loss aid with some degree of success. However, it is unknown what role guarana played in achieving these results.

• In some sensitive individuals, guarana may produce CNS stimulant-related side-effects, such as elevated heart rate and blood pressure, tremor, restlessness and excitability.

• Guarana also shows antimicrobial and chemoprotective activities in preliminary studies.

Answers to Patients’ Frequently Asked Questions

What will this herb do for me?

Guarana is a herbal stimulant that increases alertness, cognitive function and possibly mood.

When will it start to work?

Effects are expected 1-2 hours after ingestion, although this will vary depending on the individual and the current level of wakefulness.

Are there any safety issues?

Used in small amounts, it is likely to have a degree of stimulant activity and decrease fatigue; however, as with all stimulants, excessive use or long-term use can be detrimental to health. Guarana should be used with caution in people with hypertension, anxiety states, gastric ulcers, diabetes and some types of cardiovascular disease. It may also interact with a variety of medicines and therefore it is recommended to consult your healthcare professional if you are currently taking pharmaceutical medication.