Guarana extract is an herbal ingredient culled from an evergreen vine found in South America. Guarana’s main component is caffeine, reports Drugs.com, and it contains caffeine in high concentrations. It is frequently used as a central nervous system stimulant or appetite suppressant in herbal diet formulations. Before taking a diet pill containing guarana, you should talk to your doctor. You should avoid taking guarana in any supplement that combines it with ephedrine, advises Drugs.com, or if you have high blood pressure, heart disease or sensitivity to caffeine.

Anxiety or Jitteriness

You may find that due to its high caffeine content, guarana may cause you to feel anxious, jittery or “speeded up” in an uncomfortable way, reports Drugs.com. You may also feel irritable or on edge. Health Learning Info.org adds that other similar reactions may include trembling and hyperactivity. You should contact your doctor about discontinuing guarana if you are experiencing these effects in a severe or ongoing way.