I share your concern-since I bought Dr. Clark's Book on Cancer.
I would probably stick more with products that are from smaller companies as compared to top well known companies. The big companies that rub elbows with all the drug companies all use solvents.
I would also stick with things in capsules rather than in tablet form also and if you can get the toll-free numbers from the bottle, I would call to ask the company executives which solvents were used.
Dont ask "Do you use any solvents?" ask, "Which solvents do you use as I have allergies to various solvents" This way you back them into a corner and if they dont use any , they'll tell you.
If you can, buy from herbalists that make thier own stuff.
MH from the Barefoot Herbalist makes his own stuff- and refuses to use any solvents and additives. He even makes his own Oil of Oregano from the correct form of Oregano plant. The stuff is pretty strong too-
He not only makes his own herbs, but also calcium/mineral supplements, teas, etc.
it is a hobby for him.-- call at (937-666-6107 ) to order.