Is EO ingestion safe??

​Many questions from people in DoTerra or Young Living who are concerned about taking essential oils internally... The question to ask is - please show me the CLINICAL research that shows ingestion of oils like this is SAFE and EFFECTIVE. 
My comments are these: if you are a healthy adult who is not taking any medications or other herbal/ vitamin supplements, and you put one drop of an essential oil into a glass of water, and drink it, the worst that is likely to happen is that your lips, tongue, mouth and throat will be irritated by the oil and you will experience pain for about 20 minutes (perhaps longer), that will reduce if you drink a glass of full-fat milk afterwards. Oil doesn't dissolve in water, but the fat in the milk should help remove the essential oil from the tissues. 
If you repeat this several times in a day, you will be consuming more of that essential oil than you would ever likely consume in food or drink in one day, and although the essential oils are given GRAS status (Generally Recognised As Safe), this only means Safe at the levels consumed in the average American diet. In other words, we actually don't know for sure if ingestion of essential oils as recommended by those companies is SAFE. We also don't know the effects of taking essential oils every day for several weeks, months or years. The research has not been done... yet... 
My main concern is when essential oils are taken by people who have serious diseases, and who are taking other drugs, or who are children or elderly. Because essential oils have to be processed by the liver and kidneys, like other drugs, there is a chance for 1) alteration of the function of the other drugs that the person is taking 2) increased toxicity of the essential oils or the other drugs because the liver can be overwhelmed by having to process so much 3) we don't have the evidence that ingested essential oils are safe in combination with other drugs, or in people with serious disease (cancer, hepatitis, diabetes, cardiovascular disease, asthma, clinical depression). 
The question to ask is - please show me the CLINICAL research that shows ingestion of oils like this is SAFE and EFFECTIVE.