|Home > News > World > Science/Medical
Scientists find Prozac 'link' to brain tumours
By Steve Connor Science Editor
26 March 2002
Scientists have discovered that Prozac, the antidepressant taken
by millions of people around the world, may stimulate the growth of
brain tumours by blocking the body's natural ability to kill cancer
An international team of researchers led by John Gordon,
professor of immunology at Birmingham University, found evidence to
suggest cancer cells can be killed by "positive thinking", which
could be blocked when people take Prozac.
The study, to be published in the journal Blood next week,
examined the effects of Prozac and other antidepressants on a group
of tumour cells growing in a test tube. The researchers found that
the drug prevented the cancer cells from committing "suicide",
thereby leading to a more vigorous growth of the tumours.
Although an increased risk of cancer has not so far been detected
in Prozac patients, the latest findings could lead to a global
re-evaluation of the drug's long-term safety.
Prozac, a "happiness pill" that was first approved in the United
States in 1987, is widely used for the treatment of depression,
obsessive-compulsive disorder and bulimia nervosa. Doctors in
Britain issue about three million prescriptions for it each year and
worldwide sales reached £1.8bn in 1999.
Professor Gordon, whose study was jointly funded by Birmingham
University and the Medical Research Council, emphasised that the
results of his study cannot be taken as proof that Prozac stimulates
the growth of tumours.
He said: "Although that extrapolation could be valid, there is no
direct evidence from large-scale epidemiological studies currently
to back it up. However, it's important that we look again and
The research work was designed to find new ways of treating
lymphomas, a type of blood cancer, by investigating how the brain
communicates with the immune system to induce "positive thinking"
through a neuro-transmitter in the brain called serotonin.
"Serotonin is a natural chemical that regulates people's moods,
keeping them balanced. Too much serotonin affects appetite and sleep
and too little affects the mood – often causing depression,"
Professor Gordon said.
Prozac, along with other members of the class of antidepressants
known as selective serotonin re-uptake inhibitors (SSRIs), works by
preventing serotonin from being quickly reabsorbed by nerve cells in
The scientists tested other SSRIs such as Paxil and Celexa and
found they, too, had the same effect in stimulating the growth of a
type of tumour known as Burkitt's lymphoma.
"An exciting property of serotonin is that it can tell some cells
to self-destruct. We have found that serotonin can get inside the
lymphoma cells and instruct them to commit suicide, thereby
providing the potential for an effective therapy," Professor Gordon
The researchers found that Prozac blocked the entry of serotonin
into the test-tube tumour cells and therefore stopped them from
committing suicide. That raised the question of whether Prozac can
do the same in the brains of people taking the drug.
Professor Gordon said it was still premature to suggest that the
drug was unsafe. "We must stress the effects shown for the SSRI on
cancer cells is indirect and should cause no concern whatsoever to
the many millions of people throughout the world who are prescribed
this class of antidepressants," he said.
Further work is underway to test Prozac further in this field. In
particular, the scientists want to develop drugs that will mimic the
cancer-destroying feature of serotonin which is blocked by
A spokeswoman for Eli Lilly, the manufacturer of Prozac, said
that the research is too new for the company to make a detailed
response. "It's not something we can directly comment on because we
haven't been involved in it," she said.
Also from the Science/Medical section. Europe
agrees to fund rival to US navigation system
next step in human evolution
acquitted on blood pressure charge
thumbs a Darwinian advantage, study says
traces roots back to Stone Age