Can Melatonin be an effective replacement for Nyquil?

My best friend, whom I have known for years and years, has just recently experienced an extremely bad break up and has a lot of trouble getting to sleep at night. Lately, he has been taking a "shot" of Nyqil to help him get to sleep. Will Melatonin be as effective as Nyquil is? if so, what's the dosage he should take? I don't want him to turn to alcohol later on (he's only 20).