There have been two studies which indicate that regular consumption of alcohol may actually make you less susceptible to getting colds in the first place (with caveats). The first study was conducted by Carnegie Mellon University in 1993 to see the relation between smoking, drinking, and susceptibility to the common cold. 391 subjects were "intentionally exposed to one of five respiratory viruses and 26 subjects given saline." The study concluded that smokers got sick more often, people who were smokers and drinkers got sick a normal amount, and people who just drank got sick less than the others.

The other study found somewhat different results. Published in 2001, the study looked at 4,272 faculty and staff of five Spanish universities. It found that alcohol intake in the form of beer and spirits had no effect whatsoever on a persons susceptibility to the common cold. However, the study concluded that people who drank more than 14 glasses of wine per week were a whopping 60 percent less likely to get sick, even more so for drinkers of red wine. That is a huge number. It is suspected, however, that it isn't the alcohol directly, but rather the high levels of antioxidants which are in the wine. If that's the case then drinkers of Guinness and other dark beers (which are high in similar antioxidants) might net similar benefits. It must be said, though, that 14 glasses of wine per week is not an insignificant amount (two per night, on average), and of course, there may be health risks that outweigh the cold-fighting benefits for some people.