Coricidin is an over the counter medication. Some stores keep them behind the counter and require you to have an ID to purchase, you can still buy virtually as much as you want though.

The first couple times I did it were alright but every other time seemed pointless since I don't like the effects.
You definately don't want to do it everyday, dxm fucks with your mind and the other active ingredient in coricidin fucks with your body.