I think that this study with Ambien is the first to actually be directly measuring the impact of any drugs on how well the glymphatic system clears proteins and other debris. The implication for drugs (like full benzodiazepines) that reduce deep NREM sleep is that they might also impair the glymphatic system. But substances like melatonin that interfere less with sleep architecture MAY be safer in this regard, but it's mostly speculation at this point.