It is, technically speaking, a partial agonist/antagonist. This gives it some properties like Narcan(tm) or Naloxone
, the opiates that are full antagonists. An antagonist will flush out any other opiates that might be in your system, hence the use of Narcan as an antidote to overdose. It also has some properties of an agonist, which is why it blocks most WD symptoms, and also gives you that funny fuzzy-headed, bad cough-syrup, too much coffee kind of feeling sometimes.