Neuromuscular junction development is the key process required for successful neuromuscular transmission and functional innervation of skeletal muscle fibres. Various substances can influence these processes, some of which are in common use in clinical practice. In the present study, the effects of the potentially new therapeutic agent agrin were followed, along with the widely used glucocorticoid dexamethasone. The in vitro experimental model used was functional innervation and constitutive interleukin 6 (IL-6) secretion of human muscle cells. Additionally, the selective relaxant binding agent sugammadex and its possible interaction with dexamethasone were followed. Dexamethasone impaired functional innervation while agrin had opposing effects. Furthermore, based on interference with IL-6 secretion, we show potential (chemical) interactions between dexamethasone and sugammadex. The physiological effects of this interaction should be taken into consideration under clinical conditions where these two drugs might be applied simultaneously.