How would flying drones be useful to a drug runner? Their priorities are to transport a large amount of material over a long distance and to avoid detection. Drones have a relatively low payload capacity, have limited range, and are easily detected - they're not practical.
(A very different kind of "drone" has seen quite a bit of use in drug running - remote-controlled submarines! They've proven able to carry a large load over a long distance while remaining hard to detect.)
There are commercially available drones that can carry a payload of high-single-digit to low-double-digit kilograms for at least 10km.[1] They fly low enough and are small enough to avoid most radar.
Their use in cross border smuggling of weapons and drugs is well documented[2]; interception rate is low enough that they can make multiple runs before being downed, and they can pay back their purchase cost with only a few successful runs. Typical concept of operations is similar to manned ground crossings, but with drones covering the most dangerous 5-10km of actually crossing the border: a team on one side loads them up and sends them to a team on the other side, with both having a LOT of real estate to hide in because of the drone's range.
(I work on counter drone EW, and border-control customers are under intense pressure to get this under control.)
(A very different kind of "drone" has seen quite a bit of use in drug running - remote-controlled submarines! They've proven able to carry a large load over a long distance while remaining hard to detect.)