Guarana, like other sources of caffeine (e.g., coffee and tea), is recognized to be a safe plant with a long history of use. Although complications and complaints are rare, side effects are possible in some cases.
For example, guarana can affect blood pressure, so it may have a negative impact if you’re sensitive to caffeine or have blood pressure concerns. Additionally, ingesting too much of the ingredient can cause jitters and contribute to caffeine crashes, while taking it too late in the day can mess with your beauty sleep.
As Naidoo notes, we all react to caffeine differently, largely due to the uniqueness of our liver metabolism genetics, as well as our individualized gut microbiomes. That said, it’s important to pay attention to how you react to caffeine-containing ingredients—guarana or otherwise—and use that information to personalize the quantity and timing of your intake.
To play it safe, avoid high doses of guarana, as you don’t need much to reap the benefits. “Typically, a dose of less than 100 milligrams is enough to provide benefits,” notes Pasquariello. It’s also a good idea to consult your health care provider before adding guarana to your routine, just as you would with any supplement, she adds.