Methadone Is Thought to Be Effective Because It

Methadone is thought to be effective because it

A) blocks just 25-35 percent of opioid receptor sites, enough to prevent cravings for these drugs over extended periods of time.
B) binds to narcotic analgesic molecules in the blood, preventing them from forming chemical bonds with blood proteins and thus being more easily removed from the circulation.
C) is able to block 50 percent of the mu receptor sites without activating them.
D) activates only the kappa opioid receptor sites, causing dysphoria should the individual abuse opioids.