The Hangover Part II did not have the full support of my entire cast and crew." Liam Neeson replaced Gibson after being invited by Cooper, who worked with Neeson on "The A-Team", to take the part. Neeson, a fan of the first film stated, "I just got a call to do a one-day shoot on 'Hangover 2' as a tattooist in Thailand, and that's all I know about it". Gibson was reportedly furious over the decision. A source close to Gibson stated, "He doesn't understand why Mike Tyson, a drug user who turned his life around, was given a chance while Mel was kicked
Hangover research of alcohol hangover is growing rapidly. The Alcohol Hangover Research Group had its inaugural meeting in June 2010 as part of the Research Society on Alcoholism (RSA) 33rd Annual Scientific Meeting in San Antonio, Texas. In 2012, Éduc'alcool, a Quebec-based non-profit organization that aims to educate the public on the responsible use of alcohol, published a report noting hangovers have long-lasting effects that inhibit the drinker's capabilities a full 24 hours after heavy drinking. In 2012, Las Vegas based Hangover Heaven, a mobile hangover treatment clinic, opened along with its Hangover Research Institute, which studies the treatment of hangovers.