If you are talking about co-crystallizates where both compounds are in the same crystall structure: That's very, very uncommon (non-existing for your purposes ). From time to time you get solvent or water incorporated into the lattice.
If that is true, how is it that so much methamphetamine sold "on the street" is a mixture of MSM and methamphetamine within the same crystalline structure? You can purchase shards of street-grade meth that looks like 4-5mm shards of glass but it most definitely has both MSM and Methamphetamine in there.
The MSM is probably acting like a solvent. I doubt those shards are crystals but more like an amorphous ice cube with meth dissolved in it.
That makes a lot of sense.. when attempting to vaporize meth sold in the street (supposedly "good shit", big pretty crystals) the crystals turn to a considerable amount of what looks like water, but is probably MSM.. when vaporizing better-than-street-grade meth, only a small amount of liquification is noticed.