I was prescribed Ensure Plus five years ago and couldn't figure out why I kept craving it. Turns out it contains milk protein concentrate - in other words, casein, what has been found to be as addictive as hard drugs in research studies (see link in comments section). This is a natural ingredient in milk and addictive by nature - it's the way Mother Nature keeps calves from wondering into the woods - but in Ensure, it's concentrated. It's what makes cheese so addictive. Add sugar to the mix as its third ingredient and you have a concoction that you will keep craving it - much more than soda with caffeine.
How did I find out? I was prescribed Ensure Plus after getting Hyperemesis Gravidium (extreme morning sickness, what Princess Kate had). I was unable to gain much weight as I had trouble keeping any food down. After I gave birth I drank 2-3 bottles a day to put on the 20 lbs I was underweight. It worked quickly, as expected, and I put on the 20 lbs in a few months. And kept on working. It's been five years and I'm still on 1-2 bottles a day with another 20 pounds in the last year alone. I eat a healthy diet but with the 350-700 daily calories in fat and sugar it's a losing battle.
Not convinced? My son was underweight and the pediatrician prescribed Pediasure, the children's version of Ensure. He's had a bottle in the morning and in the evening. He's been on it for almost five years as well. After finding out about the addictive quality of casein, I tried to make him stop - but he too craves it. It's hard to force him to break a habit I myself struggle with. We're down to a bottle a day, supplementing his diet with whole-milk yogurt and eggs, a healthier source of protein.
The ingredients listed on amazon's Ensure Plus page do not correspond to the product's actual ingredients: Water, Corn Maltodextrin, Sugar, Milk Protein Concentrate, Canola Oil, Corn Oil, Soy Protein Isolate with than 0.5% of other ingredients. Amazon's description (as of today) is completely different: "U-D Water, Sugar (Sucrose), Corn Syrup, Maltodextrin (Corn), Calcium Caseinate, High-Oleic Safflower Oil, Canola Oil, Soy Protein Isolate, Whey Protein Concentrate, Corn Oil, Natural And Artificial Flavor, Soy Lecithin, Carrageenan And Lutein. Vitamins An"
I wanted to put this out there as a warning about this ingredient, if you have been prescribed 2+ bottles a day. It's an expensive habit, difficult to break and there are healthier options out there