Hi jfh,
YES, Activated Charcoal Powder will indeed INTERFERE with the absorption of Drugs/Medications. If you are going to take these TOXIC substances, then you must take them first and then wait at least 1-2 hours before drinking a glass of Charcoal Slurry.
Charcoal capsules don't ALWAYS dissolve in the stomach and intestines and even if they did, you'd need to take 4-6 capsules to take the place of one teaspoon of Charcoal Powder, and that would of course get costlier, if you're dealing with a SERIOUS illness.