Are all dietary supplements in pharmacies authentic?

If I understand correctly, you suspect that the supplement you bought has an uncertain origin or is "fake". What are the reasons for the doubts? If a supplement isn't available for purchase online, it doesn't necessarily mean it's inauthentic — perhaps the manufacturer isn't selling online. You can go to the pharmacy where you bought it and tell about your doubts. The staff will certainly present the manufacturer and the origin of the preparation. If, on the other hand, you mean a quality defect of the product, you have the right to a refund, which is described in the article: https://www.gdziepolek.pl/artykuly/kiedy-lek-mozna-zwrocic-do-apteki