Guarana is an ingredient in many diet supplements and energy drinks, and it is marketed as a "natural" form of energy. Many people mistakenly believe that natural ingredients are inherently safe, which is not true. And while guarana is an energy source, it also contains high amounts of caffeine, which can deliver energy, but safety becomes an issue.
There is no proven safe or effective dose for guarana. Your best bet is to follow the instructions on your pill bottle, because the manufacturer created the dosing instructions for the concentration of guarana in your particular supplement. Supplements are not regulated by the U.S. Food and Drug Administration, so there is no standardized concentration or dose timing. Each supplement maker is left to find the dose that makes its pill effective without endangering the person taking it.
Guarana's effectiveness as a treatment for obesity remains unclear, but it is an effective stimulant. The seeds contain up to 2.5 times as much caffeine as an equivalent dry weight of coffee beans. There has been some success when guarana has been used in conjunction with ma huang in weight-loss studies, but the trials have all been too short to determine long-term safety and effectiveness. Anecdotally, stimulants may help you work out harder, which may help you burn more calories than you otherwise would. But harder workouts can also increase your appetite, and you run the risk of negating your entire workout with a single meal.
If you are sensitive to caffeine, you should not take any supplement or drink any beverage that contains guarana. The "Medical Journal of Australia" reported a case of sudden death in a 25-year old woman who suffered cardiac arrest after drinking a beverage found to contain guarana at the concentration of 10 g/L -- over 60 times the caffeine content in cola. If you experience tremors, shortness of breath or chest pains after taking guarana, seek medical attention immediately.
Regular exercise and a balanced diet will keep your energy levels up. If you find that you absolutely need a caffeine boost, start the day with a cup of coffee, or drink tea throughout the day. Energy drinks are usually sugar-laden and high in calories, and the crash comes very soon after the high. Moderate aerobic activity first thing in the morning can help you have more energy throughout the day, and eating several small meals instead of three big ones keeps your blood sugar from dipping too low and causing drowsiness.