Some powders are soluble in water, and some do better in PG or in alcohol. I got a batch of tianeptine and my first water solution worked just fine. This time I added just a couple drops of Mio for flavor, and it's all gummed up! I don't know if the PG is the problem or some other ingredient. I'm pissed tho cause I've just wasted 1.5g of tianeptine. I can't get it to do anything, I added more water, shook it, heated it, and it just gets stickier.
Update: in the next batch I used plain water, and once again it dissolved beautifully. THEN I added a little Mio (cause tianeptine tastes awful), and it instantly clumped up again! So I don't know if it's the PG or what. But I am sticking to plain water with this powder.