Many people believe alcohol is less dangerous than other drugs.  Or even, don't believe alcohol is a drug at all.  Actually, there are more deaths associated with cigarettes and alcohol than with any other drugs.  One of the reasons it is one of the most substances to quit once addicted is because there is not societal stigma against alcohol like there is against other drugs.   Also, withdrawal is incredibly uncomfortable and can even be deadly--hence the need for detox in a hospital.  Finally, alcohol, like other drugs, makes long-lasting changes in the brain that change the way individuals respond to alcohol.  It typically takes a very strong network of people to support an individual in stopping drinking because cues for relapse are everywhere from the billboard to the grocery store.  So, in a nutshell, yes, alcohol is one the most difficult drugs to quit once addicted.