Most commercial vitamins use fillers such as coal tar, sand, dirt, and soap to bind the vitamins together. Here are some tests you can do to check the quality of the vitamins you use.
Take a glass and put 3 inches or so of white vinegar in it. Drop one of your vitamins in the glass. Come back after 20 minutes. Here are your items to check.
If the vitamin capsule/tablet (and its contents) has not dissolved in the vinegar, it is not dissolving in your stomach either. It is really passing through your body on its way to the sewer system. There have been doctors who have seen x-rays of a well-known multi-vitamin in its original form in the intestinal tract, and you can still read the label.
If there is dirt floating on the top of the vinegar, then the manufacturer is using sawdust as a filler. If there is grit in the bottom of the glass, the manufacturer is using sand as a filler. If there is dirt floating on the top of the vinegar, then the manufacturer is using sawdust as a filler.
If you really want to continue this experiment, wrap your vitamin in aluminum foil and bake it in the oven for a few minutes on 350 degrees. If it turns black, the manufacturer is using coal tar as a filler.
Don't be fooled by the term "pharmaceutical grade." All that means is that the manufacturer has listed on the bottle what is in the supplement. It has no bearing on the value of the contents. Vitamin manufacturers can use these harmful ingredients as fillers because the FDA does not require that the ingredient list contain the fillers that were used in the product. The only requirement is that the active ingredients in the product be listed.