Some 25 million Americans have taken antidepressants for a decade or more, and withdrawals from the popular drugs may be keeping many of them from weaning off.

There are 40 million American adults struggling with depression, 13 percent of the country's population take antidepressants, and 25 percent of those have been taking them for more than 10 years.

But how many people who try to quit the mood-altering drugs experience withdrawals? 'Absolutely no one knows,' says Dr David Cohen, a University of California, Los Angeles professor of social work and one of the few trying to fill this informational gap.

Withdrawal symptoms closely mimic depression itself, meaning that few many Americans who struggle after quitting antidepressants wind up back on them and in an endless cycle of drugs and depression symptoms.

On quarter of people who took antidepressants had been on them for 10 or more years, according to the latest CDC data, and experts say many may suffer withdrawals if they quit

There are nine major types of antidepressants. Each particular drug within those categories comes comes with its own benefits, drawbacks, side effects and chemical profile that makes it a good fit for some people and a poor one for others.

Each category acts on different individual or groups of neurotransmitters, but the principal is similar: each tries to keep levels one or more chemical elevated to improve connections between areas of the brain that regulate mood.

Antidepressants and their effectiveness have been hotly debated for decades, but lately the news for the $15 billion industry has mostly been favorable.

In February, a large UK study proclaimed that the drugs work, with 60 percent of its respondents reporting that they saw a 50 percent improvement in their symptoms within two months of taking the drugs.

Yet, even that overwhelmingly positive study found that 80 percent of people who were prescribed antidepressants stopped taking them after a month.

But there is no telling how many that quit - that early or years later - experienced withdrawals because 'no one solid study has ever queried that issue properly,' Dr Cohen says.

'This is probably because it's an unpopular issue. Drugs are presumed to be things that people need and, generally, funding [entities] are not interested as a rule in the darker side of the effect of drugs,' he adds.

Admittedly, even if the interest and funding were available, antidepressant withdrawals are hard to identify, much less study.

'Withdrawal usually resembles the problem for which the drug was originally prescribed,' says Dr Cohen.

These symptoms include general feelings of depression, 'crying excessively,' having compulsive thoughts, ideas and thoughts of self-harm or suicide, having out-of-body experiences and feeling agitated or sleepy.

We just have to pay more attention to the stories people tell. That doesn't mean we have to believe them right off the bat, just don't discount them either, and pay good, scientific, clinical attention Dr David Cohen, UCLA professor of social work

Often, people having the withdrawals will even have neurological symptoms, including 'brain zaps,' burning and tingling sensations, on top of high anxiety levels, Dr Cohen says.

In these instances, 'what is usually called a psychological or mental disorder is being manifested, but it appears as a consequence just of the way that the drug is withdrawn or is leaving the body, so it's hard to separate which is which,' concedes Dr Cohen.

Difficult, but not impossible, and how to distinguish between the two is 'the key question on which there are practically no studies,' he says.

In his clinical practice, methods have been effective to assess whether or not someone is having withdrawals.

'It's all about the history,' says Dr Cohen. 'You have got to take the individual history of the person and very carefully figure out what happened and when,' he says.

This careful documentation has the potential to reveal differences between symptoms that occurred before going on an antidepressant - which would likely be due to depression itself - and those that occurred immediately and either only or more intensely after going off the antidepressant.

The second method creates this sort of detailed history by putting the patient through the paces of medications.

Essentially, 'you note the occurrence of reactions when you give a drug, see what happens then stop the drug and see what happens. Then, you give the drug again, and see what happens,' explains Dr Cohen.

'Then, you can pretty conclusively see, because a withdrawal reaction will quickly subside when you resume the medication,' says Dr Cohen.

But this method is 'experimental,' he admits, and in fact rehashes the same kind of unending cycle that caused distress for so many patients as they tried to find the right medication to start in the first place.

'Most patients are so fed up with the process that they don't want to stop taking a medication, while others do it on their own without realizing that it's a scientifically useful process, it's exactly what a scientist would do with an animal or a person,' says Dr Cohen.

Unfortunately, providers will often simply mistake what may well be antidepressant withdrawals for a patient's need to get back on the drugs.

'If withdrawal reactions are genuine, regardless of how frequent, the worst thing is to put the person back on the drug, and say, "okay, then they shouldn't get off,"' without more carefully considering whether or not they might be experiencing withdrawals. says Dr Cohen.

Instead, he says that, if anything, they should go back on the drug only to taper off again more gradually and 'with the support and education of the person and the provider, preparing them for what to expect you would probably get rid of 90 percent of the surprise, pain and discomfort,' patients experience when they come off antidepressants.

Instead, he says that patients regularly report that they were 'extremely surprised' by their withdrawal symptoms, and 'patients, clinicians, researchers and study sponsors...everyone is in the dark.'

So like any good citizens of the modern age, patients are turning to each other and the internet to help them wean off antidepressants.

Dr Cohen and his colleagues recently conducted a survey of people who had taken antidepressants for more than nine years and decided they were ready to quit.

'They rated their relatives, sources on internet and friends who had been through antidepressant cessation the most helpful resources, bar none, and physicians were rated as much less helpful,' says Dr Cohen.

Self-managed dose-cutting has become so popular, in fact, that Cinderella Therapeutics in the Netherlands now sells tapering kits that show people how to cut down their dosages over time, depending on the specific drug and starting dosage they take.

Most of Dr Cohen's survey respondents had stopped taking antidepressants over the course of one to six months, and about 80 percent were 'real satisfied with what they had done,' he says.

'So there is a user wisdom that is emerging and being collected in some websites, and that should be used,' he says.

In the absence of resources for studies, Dr Cohen says that practitioners like himself 'just have to pay more attention to the stories people tell.

That doesn't mean we have to believe them right off the bat, just don't discount them either, and pay good, scientific, clinical attention,' says Dr Cohen.

Because, often, 'that’s what happens with withdrawal: it’s discounted.

'Instead, there needs to be a much more even-handed approach to the effects of the drugs, not just antidepressants, which often harm people more and are real difficult to get off of, more than any illicit drug,' says Dr Cohen, 'and the effects can last a year, or two, and sometimes even appear to be permanent.'