For example, it called for a ban on tobacco in the United Kingdom in 2003, expressed support for Gaza during the 2014 Israel-Gaza conflict, and issued an apology for sexist language.

Amanda Sandford, spokesperson for the anti-tobacco group Action on Smoking and Health, stated that criminalising a behaviour 26% of the population commit "is ludicrous."

Director Simon Clark called the journal "fascist," and argued that it is hypocritical to ban tobacco while allowing unhealthy junk foods, alcohol consumption, and participation in extreme sports.

[16] As reported in The Daily Telegraph, the letter "condemned Israel in the strongest possible terms, but strikingly made no mention of Hamas' atrocities.

"[17] According to Haaretz, the authors of the letter include doctors who "are apparently sympathetic to the views of David Duke, a white supremacist and former Ku Klux Klan Grand Wizard.

"[18] One of the doctors responded by saying that the letter was a legitimate exercise in freedom of expression, while a second one stated that he had no knowledge about David Duke or the Ku Klux Klan.

[27] In June 2024, The Lancet wrote an op-ed stating that "SARS-CoV-2 is a natural virus that found its way into humans through mundane contact with infected wildlife" and that "doubling down on flawed assumptions in the face of growing evidence calls motivations into question.

The quotation drew strong criticism on Twitter accusing The Lancet of sexism, arguing that this language was "dehumanising" and an "unhelpful" attempt at inclusivity.

[31][32] On July 5, 2024, The Lancet published in its Correspondence section a letter with an estimate of the number of direct and indirect deaths that may be caused in the coming months and years by the Israel–Hamas war.

[39][40] The letter has been criticized by the Chair of "Every Casualty Counts" network Michael Spagat, who wrote that the estimate "lacks a solid foundation and is implausible".

[42] Consequently, American Jewish Committee called The Lancet to "remove the letter from its website and, moving forward, exercise greater caution in selecting the claims it amplifies".

"[52] Starting in 2011, critics of the studies filed Freedom of Information Act requests to get access to the authors' primary data, in order to learn what the trial's results would have been under the original protocol.

In 2016, some of the data was released, which allowed calculation of results based on the original protocol and found that additional treatment led to no significant improvement in recovery rates over the control group.

[53][54] The results from the PACE trial have been used to promote graded exercise therapy; however, these recommendations are now viewed by most public health bodies as outdated and highly harmful to ME/CFS patients.

[55][56][57] In May 2020, The Lancet published a metastudy by Mandeep R. Mehra of the Harvard Medical School and Sapan S. Desai of Surgisphere Corporation, which concluded that the malaria drugs hydroxychloroquine and chloroquine did not improve the condition of COVID-19 patients, and may have harmed some of them.

[58] In response to concerns raised by members of the scientific community and the media about the veracity of the data and analyses,[59][60][61] The Lancet decided to launch an independent third party investigation of Surgisphere and the metastudy.

[58][63][64] As a step to increase quality control, the editors of The Lancet Group announced changes to the editorial policy in a comment titled "Learning from a retraction" which was published on September 22, 2020.

[65][66] In September 2022, The Lancet published the report of their "Covid-19 Commission" which was headed by Jeffrey Sachs, an economist with no medical background, who has pushed the conspiracy theory that Covid came from a US "biotechnology" lab.

Virologist Angela Rasmussen commented that this may have been "one of The Lancet's most shameful moments regarding its role as a steward and leader in communicating crucial findings about science and medicine".

These papers, which discussed the first tissue-engineered trachea transplant, were found to contain fabricated information following an investigation by the Swedish National Board for Assessment of Research Misconduct.