(13)A significant number of other substances, many of them traded legally in large quantities, have been identified as precursors to the illicit manufacture of synthetic drugs and psychotropic substances. To subject these substances to the same strict controls as those listed in Annex I would present an unnecessary obstacle to trade involving licences to operate and documentation of transactions. Therefore, a more flexible mechanism at Community level should be established whereby the competent authorities in the Member States are notified of such transactions.