Many years ago I rented a backhoe and excavated all the dirt around the outside of our basement (foundation), so that I could seal it well. I put all the extra dirt in a pile at the edge of the property. I had access to as much free old horse manure as I wanted, so I decided to backfill with the horse manure compost, for the following reasons: 1) to allow rainwater to more easily pass from the surface down to the french drain which runs around the outside of the footing (previously it was mostly clay); 2) I did not want to have to rent the backhoe again; 3) to be able to plant in 7 feet of rich compost
. The earthworms went crazy in the compost, reproducing like mad. When we had heavy rain, to avoid drowning the earthworms climbed up the side of the house, and on occasion through the drains in the windows, into the house, down the wall, and across the carpet... For a few weeks we would come home to 1 or 2 dehydrated worms in the middle of the living room, which did not make my wife too happy.
But the "worm bloom" passed, leaving beautiful compost soil.
So anyway if there were drugs in the manure, they sure did not hurt the earthworms.