Well, yes, tea bags can be used to treat dark circles under eyes. For example, you can make tea bags cool and then apply them on your eyes. And just repeat it for a long time. And then it can be effective, for cool tea bags contain a lot of nutrients, it can help to relax the eye muscle and then, dark circles can be relieved. According to some experts, you can just try some sesame oil, which contains a lot of nutrients such as vitamin e which are good for the dark circles under eyes. By the way, heating a piece of garlic will work wonders if done right. And then you can just put heated garlic on eye and hold until garlic cools. And then just repeat the process for a while. And you need to have a good rest too. Anyway, just have a try.