article in BMC (an academic journal) has found that a large portion of herbal substances contain none of the herbs they're supposed to contain, contain related herbs that are toxic, and/or contain fillers that cause allergies in many people. Since many of these herbs haven't been shown to work in the first place or aren't effective in the small doses shoved inside a capsule, this news is just one more reason for all of us to reconsider whether these pills are really worth the money. This is from the article's results section:
We recovered DNA barcodes from most herbal products (91%) and all leaf samples (100%), with 95% species resolution using a tiered approach (rbcL + ITS2). Most (59%) of the products tested contained DNA barcodes from plant species not listed on the labels. Although we were able to authenticate almost half (48%) of the products, one-third of these also contained contaminants and or fillers not listed on the label. Product substitution occurred in 30/44 of the products tested and only 2/12 companies had products without any substitution, contamination or fillers. Some of the contaminants we found pose serious health risks to consumers.