Quote:
the placebo effect is bigger than the drug's effect and
This is simply incorrect. The graph reflects net change in drinking, so a lower line means less drinking. Nal was MORE effective than placebo at helping control drinking, as stated in the abstract.
Of course it is correct. Once again, for professional scientists among us:
On placebo: reduction of ~ 2 units
On naltrexone: reduction of ~ 3 units
Now, those who take Naltrexone are subject to placebo effect just the same as those who take sham control. Therefore, the Naltrexone-specific, placebo-independent effect is 3-2=1 unit. I.e., placebo effect of ~ 2 units is obviously higher than naltrexone effect of ~ 1 unit.
This is basic stuff... Now, you could argue that placebo and drug effects might not be simply additive. But the placebo and drug interaction is never antagonistic. It is either additive or synergistic (in the latter case the placebo-independent naltrexone effect would be even smaller).
See:
http://www.jneurosci.org/content/32/23/8053.abstract(argues for pure additivity)
http://www.trialsjournal.com/content/11/1/110(argues for a new mechanism of synergism)