Taking different vitamin capsules at the same time is usually fine. There are a few exceptions which can help you decide what you should take together, what foods will help best absorb vitamins, and when you should avoid taking different vitamin capsules together. Essentially only a few vitamins and minerals inhibit absorption of each other.

Iron, technically a mineral and not a vitamin is usually best not taken with other vitamin capsules, or at least with any supplements that may contain calcium. It’s a good idea to take iron with vitamin C, which can actually help you better absorb iron. So it's fine to take different vitamin capsules together if one is iron and the other does not contain calcium. It can also help to take iron with foods that contain lactic acid, or foods that contain citric acid, like orange juice. Don’t take your iron with milk, but you can, ironically, take it with yogurt.

It also can be important to take certain different vitamin capsules with foods that will best absorb them. For instance, vitamins D, A, and E are all fat soluble, and best taken with a meal that contains fat. If you’re using milk as your fat source, you’ll again want to avoid taking an iron supplement at the same time.

It can be a mistake to take different vitamin capsules with other medications you may be taking. For instance if you take medications for a thyroid condition, you should avoid taking any vitamins at least four hours prior to taking your thyroid medication (Synthroid, levothyroxine), and at least an hour after. Some antacids can degrade or devalue your different vitamin capsules and should not be taken with them. Further you should never take vitamins containing potassium if you are on warfarin, a common anti-coagulant medication for people with heart conditions.

It’s always best to have a physician evaluate the different vitamin capsules you plan to take to decide if they are best suited to you. A physician can evaluate your current state of health, any health conditions you might have and any medication that might not work effectively with different vitamin capsules. In most cases physicians suggest that you get most of your vitamin needs fulfilled through eating a healthy and varied diet.

Many people take more vitamin capsules than they need, taking an excess of the daily recommended amounts. Taking more than is needed usually does not work, since people usually just excrete extra vitamins through urine. Some different vitamin capsules can be highly dangerous when taken in excess, especially iron, and high doses of fat-soluble vitamin A. It’s therefore advised you take only what you need, which may amount to a small daily supplement instead of a variety of different vitamin capsules.