Not much serious research has been done on the effects of guarana. We only found something on the Web about experiments on dogs, mice and rats.

Suspected caffeine and ephedrine toxicosis resulting from ingestion of an herbal supplement containing guarana and ma huang in dogs: 47 Cases (1997-1999). (Source: Journal, American Veterinary Medical Association)

Records of dogs that had ingested an herbal supplement containing Ma Huang and Guarana between July 1997 and October 1999 were retrieved from the National Animal Poison Control Center database.

Results: Most dogs (80%) developed clinical signs of toxicosis within 8 hours of ingestion, and clinical signs persisted for up to 48 hours. Hyperactivity, tremors, seizures, and behavior changes were reported in 83% of dogs; other signs included vomiting (47%), tachycardia (30%), and hyperthermia (28%). Seventeen percent of the dogs died.

Conclusions and Clinical Relevance: Accidental ingestion of herbal supplements containing primarily Guarana and Ma Huang in dogs can lead to a potentially lethal condition that may require prompt detoxification and supportive treatment for several days. Most dogs recovered with supportive treatment.

Pharmacological activity of Guarana (Paullinia cupana) in laboratory animals.

Abstract (original article can be found here)

Mice that ingested a suspension of guarana (Paullinia cupana, Sapindaceae) in a dose of 0.3 mg/ml showed a significant increase in physical capacity when subjected to a stressful situation such as forced swimming after 100 and 200 days of treatment. Such an effect, however, was not obtained with a concentration of 3.0 mg/ml, nor with the ingestion of a suspension of ginseng 5.0 mg/ml, nor of a solution of caffeine 0.1 mg/ml. Guarana, both after a single (3.0 and 30 mg/kg) or chronic administrations (0.3 mg/ml), was able to partially reverse the amnesic effect of scopolamine as measured through a passive avoidance test in mice and rats, indicating a positive effect on memory acquisition.

However, no effect was observed when an active avoidance task was used in rats, even after 20 days of guarana administration. There was also a tendency of rats treated with 0.3 mg/ml of guarana to better maintain the memory of a Lashley III maze path. The animals had the same average lifespan, indicating a low toxicity of guarana, even after 23 months of treatment.

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