Maca is also called Peruvian Ginseng and is an adaptogen. That means that it helps the body adapt to stressful situations. Maca supports the thyroid, endocrine, immune system and the adrenal system.
It is generally thought to be safe, but it is always possible that a herb or supplement might interact with medications.
For more information on maca, see http://www.antiaginganswers.net/maca.html