Although the producers thought of Friends as "only a TV show", numerous psychologists investigated the cultural impact of Friends during the series' run. Aniston's hairstyle was nicknamed "The Rachel", and copied around the world. Joey's catchphrase, "How you doin'?", became a popular part of Western English slang, often used as a pick-up line or when greeting friends. The series also influenced the English language, according to a study by the University of Toronto that found that the characters used the emphasized word "so" to modify adjectives more often than any other intensifier. Although the preference had already made its way into the American vernacular, usage on the series may have accelerated the change. Perry's habit of ending a sentence unfinished for sarcasm also influenced viewers' speech. Following the September 11 attacks, ratings increased 17% over the previous season.

Friends is parodied in the twelfth season Murder, She Wrote episode "Murder Among Friends." In the episode, amateur sleuth Jessica Fletcher (Angela Lansbury) investigates the murder of a writer for Buds, a fictional television series about the daily lives of a group of city friends. The episode was devised after CBS moved Murder, She Wrote from its regular Sunday night timeslot to a Thursday night timeslot directly opposite Friends on NBC; Angela Lansbury was quoted by Bruce Lansbury, her brother and Murder, She Wrote's supervising producer, as having "a bit of an attitude" about the move to Thursday, but he saw the plot as "a friendly setup, no mean-spiritedness." Jerry Ludwig, the writer of the episode, researched the "flavor" of Buds by watching episodes of Friends.

The Central Perk coffee house, one of the principal settings of the series, has inspired various imitations worldwide. In 2006, Iranian businessman Mojtaba Asadian started a Central Perk franchise, registering the name in 32 countries. The decor of the coffee houses is inspired by Friends, featuring replica couches, counters, neon signage and bricks. The coffee houses also contain paintings of the various characters from the series, and televisions playing Friends episodes. James Michael Tyler, who plays the Central Perk manager in the series, Gunther, attended the grand opening of the Dubai cafe, where he worked as a waiter. Central Perk was rebuilt as part of a museum exhibit at Warner Bros. Studios, and was shown on The Ellen DeGeneres Show in October 2008. Jennifer Aniston revisited the set for the first time since the series finale in 2004. From September 24 to October 7, 2009, a Central Perk replica was based at Broadwick Street, Soho, London. The coffee house sold real coffee to customers and featured a display of Friends memorabilia and props, such as the Geller Cup from the season three episode "The One with the Football." In Beijing, business owner Du Xin opened a coffee shop named Central Perk in March 2010. There are two Friends themed cafes in Pakistan as well. One in Lahore known as "Friends Cafe" and the other in Peshawar called "Central Perk". Both of those cafes have an iconic couch,a guitar and foosball table,quotes from the show on the walls and even episode reruns on a projector. They're also planning to have their own Gunther at the bar.

Friends has also developed an alternative family lifestyle by representing young people that live unconventional domestic lives. It presents the idea that "all you need is good friends" and can construct families through choice. The audience is able to identify with the program through the troubles seen on weekly episodes. It portrays a new way of living life and developing relationships which are not normally seen in conventional society. According to a pop-culture expert at the University at Buffalo, Friends is "one of those rare shows that marked a change in American culture." The images of youth and the roles they portray are better defined and represent a lifestyle that centres around creating and sustaining relationships between friends running their own lives and seeking help from each other.