Antidepressant（抗忧郁）drugs such as Prozac were viewed in the early 1900's as wonder pills that would remove depressive blues for good. But in the past five years, growing scientific evidence has shown these drugs work for only a minority of people. And now a research journal says that these antidepressants can make many patients' depression worse. This alarming suggestion centres on the very chemical that is targeted by antidepressants-serotonin（血清素）. Drugs such as Prozac are known as selective serotonin re-uptake inhibitors（or SSRIs）. Their aim is to increase the level of this  “feel-good” chemical in the brain.
But the new research, published in the journal Frontiers In Evolutionary Psychology, points out that serotonin is like a chemical Swiss Army knife, performing a very wide range of jobs in the brain and body. And when we start changing serotonin levels purposely, it may cause a wide range of unwanted effects. These can include digestive problems and even early deaths in older people, according to the study's lead researcher Paul Andrews. “ We need to be much more cautious about use of these drugs,” says Andrews, an assistant professor of evolutionary psychology at McMaster University in Ontario, Canada.
Previous research has suggested that the drugs provide little benefit for most people with mild depression, and actively help only a few of the most severely depressed. Famous psychologist Irving Kirsch has found that for many patients, SSRIs are no more effective than a placebo pill. A research in 2010 on Danish children found a small, but significant, increase in the risk of heart problems among babies whose mothers had used SSRIs in early pregnancy. The key to understanding these side-effects is serotonin, says Andrews. Serotonin is also the reason why patients can often end up feeling still more depressed after they have finished a course of SSRI drugs. He argues that SSRI antidepressants disturb the brain, leaving the patient an even greater depression than before.
“After long use, when a patient stops taking SSRIs, the brain will lower its levels of serotonin production,” he says, adding that it also changes the way receptors in the brain respond to serotonin, making the brain less sensitive to the chemical. These changes are believed to be temporary, but studies indicate that the effects may continue for up to two years.
Most disturbingly of all, Andrews' review features three recent studies which, he says , show that elderly antidepressant users are more likely to die earlier than non-users, even after taking other important variables into account. One study, published in the British Medical Journal last year, found patients given SSRIs were more than 4 per cent more likely to die in the next year than those not on the drugs.
“Serotonin is an ancient chemical,” says Andrews. “It is regulating many different processes, and when you disturb these things, you can expect that it is going to cause some harm.”
Stafford Lightman, professor of medicine at the University of Bristol, and a leading UK expert in brain chemicals and hormones, says Andrews’ review highlights some important problems, yet it should also be taken with a pinch of salt. “This report is doing the opposite of what drug companies do,” he says. “Drug companies selectively present all the positives in their research, while this search selectively presents all the negatives that can be found. Nevertheless, Andrews' study is useful in that it is always worth pointing out that there is a downside to any medicine. ” Professor Lightman adds that there is still a great deal we don't know about SSRIs-not least what they actually do in our brains.
When it comes to understanding why the drugs work only for a limited part of patients, U.S.  scientists think they might now have the answer. They think that in many depressed patients, it’s not only the lack of feel-good serotonin causing their depression, but also a failure in the area of the brain that produces new cells throughout our lives. This area, the hippocampus, is also responsible for regulating mood and memory. Research suggests that in patients whose hippocampus has lost the ability to produce new cells, SSRIs do not bring any benefit.
According to paragraph 2, serotonin, like a chemical Swiss Army knife, can             .

A．make many patients' depression worse

B．cause a wide range of unwanted effects

C．affect human body and brain in various ways

D．provide little benefit for most depressed people

In Stafford Lightman's opinion,                    .

A．drug companies don't know the negative effect of antidepressants

B．Andrews focused on different things from the drug companies

C．scientists have found what SSRIs do in the brain

D．Andrews' research has no medical value

Which of the following is TRUE about SSRIs?

A．They are used to increase the “feel-good” medical in the brain.

B．They can work even when the hippocampus can't produce new cells.

C．They create a risk of heart problems in pregnant women.

D．They are responsible for controlling mood and memory.

What is the text mainly about?

A．The aim of drug companies

B．The function of SSRIs

C．The side-effects of antidepressants

D．The cause of depression