I dunno if it's a slippery slope... I know I'm late on response and I don't have the absolute knowledge to answer properly but only share my personal story and opinion: I abused NEP (2021, when was legal and very good quality) with a month of a-PiHP both smoked/vaped in an oil burner. I went like this 8 months straight until last 2 weeks a psychotic delusional stim induced-state possessed me. I got clean immediatly without suffer any problem. That was an issue. Years fordward they diagnose finally ADHD to me (since I was a child I suffer from it but never got a proper diagnose). After self medicating without knowing well why, but I need that, of fluoro-amphetamines and 4F-MPH I did a last binge of 10g of smoked NEP before the absolute ban. in 2024 they diagnose me ADHD and gave me methylphenidate. Until titrating process I were talking them as prescribed but around 60mg daily (now im up to 80mg daily) things get pretty wild. IVd couple of times 120mg at once, crazy euphoria, also boofed give crazy euphoria. but mainly I snorted the shit consuming up to 400-500mg daily easily. Now I'm in the shit, I tried meth, I finished a gram of meth vaped and snorted in less than 12h cause (I doesn't seems to kick in properly).
MPH is underrated, isn't a drug for taper or solve problem unless stricly following the doc prescriptions. I has so high the tolerance to MPH that meth almost gives me a rush, yes I were sharp and awake but nothing compared to NEP (which some crackheads I know prefer it over crack and meth) or even the euphoria that huge doses of MPH gave me.
Hope your process will be clean as possible without shifting from an addiction to another.