Magic is interesting aspect in H.P. Lovecraft's works, as it is not directly “magic” but more of rituals and alteration in cosmic powers. that is a interesting aspects to study and design that how it suit to game like Mythos The Awakening.
So called “magic” in Mythos is unnatural to common persons and weak minded persons could certainly got insane or least suffer varies mental damages.
In Mythos The Awakening investigators who use spells also lose some points from their sanity. Amount of sanity loss depends on success of the spell, if it success then lose only minor amount but if failure there are danger to fall insane or at least lose large amount of sanity.
Spells like Agony and Devour will work as aggressive spells which only the most strong minded is recommend to cast because of their dangerous fail effect. players can also cast protective spells which surely can deflect some of damage but also can drain casters sanity.
Spells can be obtained through rumours or by visiting one of the cities archives. Spells are expensive but important investment because some of the enemies are highly resistant to physical damage but can be killed with spells with little effort.