Aren’t the terms “drug,” as in a substance that makes you sluggish, and “drug,” as in something you towed behind you, directly related?
In Moby-Dick Melville writes of harpooning a whale with the spear’s line attached to a drug, then letting the whale pull the line and drug overboard. The drug consists of a square of wood; the harpoon line attaches at the center of the square.
So, the whalers’ drug is towed (dragged) behind the fleeing leviathan; its purpose is to wear the animal out, that is, to make him sluggish. Thus, the two seemingly unrelated meanings come from one genesis concept.
I think you’re probably right. The Old English cognate gives us draw, drew which is a strong verb. “Drag” is a later Middle English borrowing, probably from one of the Scandinavian languages. The fact that is a borrowing is probably why it was made a weak verb in the early written sources, but that’s just an educated guess on my part.
And if I remember my language history classes correctly it was most probably “dragga” at the time. The transition from a short to a long “a” sound came along around at that time.
It’s a bit hard to explain as English does not have the corresponding sounds. The best I can come up with would be gatta and gata (street as in various street names in York ending with gate) that has gone through the same transition from short to long. They are pronounce approximately like English gutter and garter respectively.
