wouldn't you want a furry friend with an addiction to powerful drugs to keep you company?
The only thing search/detection dog is addicted to is the simple pleasure of working. They're descended from wolves, who live to hunt. They're bred to be incredibly sensitive, nose-wise, and have had their pack instincts morphed into a very gratifying (for them, and their handlers) pleasure in their essentially symbiotic relationship with humans. They love to go out and do stuff, and are raised as pups to get some good clean joy out of accurately differentiating between being right and wrong with their noses. They're addicted to being part of a well organized pack, just like many social animals. Addicted to the drugs or other materials they've learned to identify by the parts-per-billion in the air? Nonsense. They want a pat on the head, their favorite toy as a reward, and a chance to go do it again.