Rhodiola Rosea has an extensive human safety record across decades of clinical use in Europe and Russia, where it has been used as a traditional adaptogen since the 1960s. At 400mg it is well within the established safe dose range. It is non-habit-forming, stimulant-free, and contains no synthetic compounds.
The most commonly reported side effect in a small number of users is mild digestive adjustment in the first few days, which typically resolves on its own.
As with any supplement, consult your healthcare provider if you are pregnant, nursing, or managing a diagnosed condition.