Birol Ünel had not been in military service in Turkey and therefore could not travel to Turkey without being arrested. However, as they say on DVD, at the last minute Turkish parliament decided on an amnesty, so he could return to his home country for the first time after 10 years and finish the movie.
In the opening scenes, where Cahit appears to be completely drunk, Birol Ünel isn't acting. He really was completely drunk, having been drinking solidly whilst waiting hours for the scene to be set up.
During filming, Birol Ünel was told by his doctor that he had to quit drinking alcohol, otherwise he could die. This accounts for Ünel's weight loss in the latter part of the film, though giving up the booze made him so ill at one point that filming had to be suspended.
The scene where Cahit is smashing glasses with his bare hands was done using chemicals: Birol Ünel's hands were covered in a substance that would turn red when reacting to the liquid in the (plastic) glasses.
As the film started to pick up awards at international film festivals, leading actress Sibel Kekilli was "outed" by the German tabloid press for being a former porn star. Kekilli responded to this by reproaching the tabloids for "media rape" at the 2004 Bambi Awards, during her acceptance speech.