There are several episodes which show explicit sex scenes with female breast & buttocks nudity.

Sex and the personal love affairs of different characters is an ongoing theme in the show.

Crude sexual terms are used very frequently.

Throughout the series, many characters get into fights.

In some episodes, people get killed in fires very gruesomely.

Several characters get shot throughout the series or are killed in various circumstances.

The show itself is laden with strong profanity, basically every profane word or phase is used except for the F word. Every episode has substantial amounts of profanity, particularly words like "goddamn", "shit", "ass", "asshole", and "prick".

The strongest language used in the series is sexual slang such as "cock", "pussy", "dick", and "tits". The word "cocksucker" is once used as an insult in a Season Two episode.

Throughout the series, crude humor, crude sexual terms, and racial/ethnic/sexual slurs are used very frequently.

The main character is a recovering, although on-an-off again alcoholic and chain smoker. Therefore, alcohol is perhaps the major theme of the entire series.

Many characters smoke cigarettes and cigars frequently.

Several characters are alcoholics.

Several characters are habitual drug users and addicts(usually prescription drugs, marijuana and cocaine on occasion).

The show revolves around the central character, a New York City Firefighter, who suffers from severe post-traumatic stress disorder(PTSD), survivor's guilt, and serious alcoholism after bearing witness to the deaths of many of his friends and fellow firefighters and the gruesome horrors he saw during the World Trade Center attack on 9/11/01.

The show itself is very intense and covers very adult topics, such as post-traumatic stress disorder(PTSD), survivor's guilt, lustful and intense sex, alcoholism and it's consequences and effects, drug addition, violence, inter-family relationships, homosexuality, and various other addictive behaviors.