This is natural "Strontium citrate" from the crust of the earth. It is not synthetic " Strontium ralenate" which is used in Europe and has many horrible side effects one of them being blood clots. My patients and customers have told me that there are some Doctors that are confused about the difference between plain Strontium as an element and Strontium ralenate a synthetic product....they also seem to be confused about the elemental Strontium that I recommend and sell and "Strontium 90" which is a by-product of exploding the Atomic Bomb. It always seems to be male Doctors that are in this confused state and tell their patients that Strontium is radioactive.....I say to all my patients and customers remember ...."boys will be boys" To my male collegues I highly recommend that you read about Strontium the element before you give your patients the wrong information and instill fear into them. Here's a great testimonial that you will love!!!! ******************************************************* Dear Dr Helen: My bone density test showed that had osteopenia. I took the Strontium and just this month had a comparison done to last year's bone density and my density was up 13%. My doctor said whatever I was to keep doing it. I told her about the Strontium and she put in my record. Thought you should know, and I am pleased it is reversing my bone loss. I also use your bioidentical hormones. Thank you. M.W.