From the MSDS of msm, it says its not toxic when inhaled. Insofar as it is a USP or equivalent grade. Otherwise, all bets are up.
i think that I'd be more concerned about the fact that you're getting 'amphetamine powder' that you believe 4-FA cut with 'MSM' speaks volumes. There are many types of 4-fa (entirely different compounds and/or the slight cut could give it entirely different properties smoked vs eaten, as well as various types of fluorinated amphetamines, their n-methylated counterparts (x-FMA) as well as their beta-hydroxylated cousins (the so called 2/3/4-fluorinated analogs of d/l/dl-(pseudo)ephedrine).
If i had to guess i mean, what's more likely - them cutting it with the unreacted x-Fluoroephedrine that likely is a precursor available in massive abundance wherever the fuck it is they make that(this would save them an extra step, production/reagent costs etc..)
Or perhaps something relatively inactive like (-)-4-FA then added to a racemic amphetamine/4-FA.. No one except experienced users who've actually had legitimate stuff would know the difference, people divvy this out by the point which is a dose for christssakes not gonna say how much but a 1/4g of speed powder here in California costs less than a Big Mac meal. Legitimate stuff often is around the same price range and impossible to be sure of the quality until it's tested. Even (especially??) long term experienced users can be fooled once they're addicted enough. It's a suckers' game.
In terms of rc cuts, For a chinese or indian lab where some % could likely result in massive profits it probably becomes clear very quickly that cutting a pure product with 50% or more peripheral-stimulating bullshit is the financially sound choice, or them shipping a pure product that then gets mixed with msm? The answer is probably both things happen unless you have a superb connect. Not to mention they all look the fucking same to the naked eye I've smoked 4-fma before, it's actually interesting because it is completely clear when it solidifies in a pipe, but then again that could have just been whatever my source cut it with seeing as how all fluorinated amphetamines are smokable..
In a perfect world where all drugs are pure the game would be way different but if you can't even verify what exactly it is you're putting in your body then it's time to change sources or look for something else