I came across an online article called "Bad Combinations For Supplements". So I would like to share some of the interesting points here. A bad combination doesn't necessarily mean harmful for the human body. One supplement may be absorbed in the body, while the other hardly at all. In that sense, it is more a 'wrong' combination than a bad one, to be exact. It is a question of when we should take those kinds of supplements. The following are examples of combinations of supplements to avoid as they counteract each other. 1) Calcium(Ca)+Iron(Fe) : If you take Fe with vitamin C, you'll need to take Ca with another meal at least two hours later. 2) Zinc(Zn)+Copper(Cu): If you take more than 25mg of Zn, you'll also have to take a few mg of Fe. 3) Iron(Fe)+Green Tea/Coffee: If you drink coffee or tea, you'll need to take Fe at least a few hours later. If you take high doses of calcium, this will prevent the human body from absorbing magnesium (Mg), iron and zinc. So does high-dose zinc. It slows down copper absorption and is one of the most problematic combinations. That's why there are some practical guidelines which can cover these kinds of issue, like not taking a single-mineral calcium supplement with a single-mineral iron or zinc supplement at the same time. This habit will help avoid potential competition between supplements. It's hard to make a time schedule for taking supplements. Instead, you'll just have to split some supplements into two groups and take each at breakfast and dinner. You should take Fe with vitamin C at breakfast and take Ca, Mg and Zn. Taking Mg just before sleep can help you relax.