Substances are not decomposed significantly by heat before reaching at least their melting point temperature. If they would, no melting point would be given in literature, as the substance in question wouldn't have one, per definition.

SWIM routinely heats his Meth.HCl to temperatures over 100°C in an oven (mp of meth.HCl is 172°C), to quickly drive off H20 or other solvents. No decomposition of product has been noticed.

Post 309268

(Rhodium: "Meth related posts go in the STIMULANTS forum!", Newbee Forum)