Medicines for animals
It is illegal to import medicines for animals from other countries. This applies whether you order the medicine online or pick it up yourself.
Even though some companies abroad sell medicines for animals online, private individuals in Denmark are not allowed to buy such medicines and have them sent to Denmark. Moreover, it is illegal to import medicines for animals to Denmark from travels abroad. It does not make any difference that the medicine comes from another EU country.
The reason is the fear of bacterial resistance among animals and humans as well as the consideration for food safety since medicines intended for pets may also be used for food-producing animals.
Read more in the Danish executive order on import of medicinal products by private individuals (in Danish).