Well, family members of presidents with prescriptions drug probs are not uncommon. As well as with alcohol and illegal drugs. My guess is Xanax or ambien. The list of presidents and governors with kids with this kind of thing is long. Doesn't seem like a national story to me unless the news need something to chew on and bash both Bushes with.
My guess is Xanax Congratulations, you win the prize, later stories say it was Xanax, what is called a 'minor' tranquilizer, but addictive.