This can be as complicated or as simple as you make it. One of the easiest ways to decide if your multivitamin is good for you is to ask yourself if you feel better when you take it? If you are actually absorbing the nutrients that it proclaims to have in it, you should be able to notice a difference in your energy level and sense of well-being.
Now, if you want to get a little more technical, you might want to ask the manufacturer if they have done bioavailability studies on their products. This is how they determine if the people that take the vitamin are actually absorbing the ‘stuff’ in it. You could also ask how they do their quality control. Do they test every batch? Do they test once a month? Once a year? Ever? A good company will not only do this testing, but also be more than happy to make it available to you.
If that seems like too much work, think about the basics. It is very difficult to stuff every nutrient you need for an entire day into one tiny pill. So typically a good multivitamin will be one that you take a few of to get the full dose. And, typically, something in a capsule is better absorbed than a tablet simply because the ingredient haven’t been compressed as much.
Next, you need to really look at the ingredients, especially the ones at the bottom listed as “other ingredients”. How many things are on that list? Are there more preservatives than nutrients in the vitamin? Exactly which types of nutrients are best is an entirely different discussion for another day, but hopefully this helps you get started.