Certain chemicals may be used for producing narcotics. These chemicals are also called drug precursors.
If you bring drug precursors into the European Union, trade, store or transport them, you should have a licence. Customs checks for the presence of these licences. If a licence is missing, Customs may intercept the shipment. You furthermore run the risk of committing an offence.
Please consult amongst other things the
Abuse of Chemical Substances (Prevention) Act (in Dutch: Wet Voorkoming Misbruik Chemicaliën. WVMC) (only available in Dutch).