Though we discovered this some time ago , there has been lingering controversy regarding it's mechanism of action in humans. Here is a controlled study consistent with k-opioid being essential target.
On-line here . A fair amount of time was spent on this to make sure key issues were addressed --especially those which may not be obvious to those who do not study GPCRs. BTW: DREADDs are engineered GPCRs......
This will be useful for determining how and to what extent canonical (G protein) vs non-canonical (arrestin) singaling is essential for the actions of a particular biological/physiological phenomenon.
A nice paper just published using the M1-DREADD which like M3 is Gq coupled to interrogate learning and memory. As predicted M1 behaves similarly to M3.