It depends where you live.
For instance in the UK it is against the law to grow it or propagate it. It is a civil liability to allow it to grow and spread to your neighbour's property. It is a criminal liability if you are causing or allowing it to grow in the wild and you are obligated to mention the plant growing on your
land when you are selling your home.
It might be wise to know the laws of your country. Isn't there another medicinal plant that could replace such an invasive species? It is not only a pesky weed but an aggressive plant that destroys flora and fauna, endangering ecosystems, especially along river banks.