I use vanilla enough and frequently. Mom and I bought few bottles of vanilla from the Dominican Republic (DR). I just finished the last one now and went online to order more. Then the fun begins. I believe the vanilla I have is pure vanilla as I was told when I was there but there is no info on the bottle, of course.
Apparently imitation vanillas imported from countries like Mexico, Nicaragua, the DR, Canada contain the ingredient Coumarin (a chemical compound and also referred to as the Tonka bean) It also depends on the company producing it if it contains the compound. Generally speaking the compound added to vanilla will come from the region of these countries.
The USDA has banned Coumarin for human consumption since the 50's due to liver toxicity and because it also causes tumors and liver cancer in rodents. It has been shown that humans process this chemical a little differently due to its chemical structure, but it still has toxicity consequences to humans.
The Germans have established a tolerable daily intake level while OSHA has not put that chemical on our chemical regulation list.
Coumarin occurs naturally in some edible plants such as strawberries, apricots and cherries. It is widely used in the fragrance industry and in fabric conditioners due to the sweet smell.
So although it is banned in food it is allowed in alcohol, some pipe tobaccos and has limited approval for few medical uses (in the US).
Bottom line, spend the money and try to only purchase pure vanilla and forgo the imitation vanilla. If you have imitation vanilla (with Coumarin), apparent use is for rat poison. Here are some articles for your review: