Following an application from Nutrilinks Sarl, submitted pursuant to Article 13(5) of Regulation (EC) No 1924/2006 via the Competent Authority of Belgium, the Panel on Dietetic Products, Nutrition and Allergies (NDA) was asked to deliver an opinion on the scientific substantiation of a health claim related to Rhodiola rosea L.extract and reduction of mental fatigue. The food constituent that is the subject of the health claim is a dry powder extract of Rhodiola rosea L., which is standardised for its content of rosavins and salidroside. The Panel considers that Rhodiola rosea L.extract is sufficiently characterised. The claimed effect is “helps to stimulate intellectual functions in situation of stress after the first intake”. Upon request by EFSA, the applicant clarified that the claimed effect related to the reduction of tiredness and fatigue in situation of stress. The target population proposed by the applicant is healthy adults in situations of fatigue and stress. The Panel considers that reduction of mental fatigue is a beneficial physiological effect. The applicant identified two published human intervention studies as pertinent to the health claim. These studies were carried out with a Rhodiola rosea L. extract which was standardised only for its salidroside content and not for its content of rosavins. The Panel notes that these studies were not undertaken with the food constituent, Rhodiola rosea L.extract, which is the subject of the health claim and which is standardised for both its rosavins and salidroside content. The Panel considers that no conclusions can be drawn from these studies for the scientific substantiation of the health claim. The Panel concludes that a cause and effect relationship has not been established between the consumption of Rhodiola rosea L.extract and reduction of mental fatigue.