Ketamine may work to treat three of the most common mental health problems - anxiety, depression and addiction - according to a new pair of studies.

The sedative has been used for anesthesia, especially by veterans, and as an illicit party drug for decades, but a growing body of research suggests it may be psychologically therapeutic, too.

For those with treatment-resistant mental health concerns, ketamine has shown promise for quickly relieving depression, and a number of clinics using the drug experimentally have popped up.

Now, two new studies from Harvard University and Yale University have found that it might work for depressed patients suffering from anxiety and addiction (respectively), too.

Two new studies from Harvard University and Yale University suggest that ketamine may work to treat depression in people who also have anxiety or addictions

Antidepressants fail to relieve persistent feelings of sadness, hopelessness and fatigue for between 10 and 15 percent of sufferers.

Plus, somewhere around 60 percent of Americans with depression are estimated to also suffer from anxiety, and vice versa.

And that complicates treatment options that may make one condition better, but worsen then other, or only treat one.

It's a frustrating conundrum for millions of people worldwide. Treatment failures can serve to just deepen feelings of hopelessness and ongoing depression in turn can even raise risks of other diseases, such as Parkinson's.

'Historically, antidepressants have not been very effective for a particular subset known as anxious depression,' explains Dr Steven Levine, a New Jersey-baed psychiatrist who now runs nine ketamine clinics.

In recent years, doctors and the scientific community at large have started to become more open-minded to novel therapies for mental health issues, perhaps out of desperation to treat their most desperate patients.

And some of the unexpected treatment contenders have been long-denigrated 'party drugs,' including the active chemical in magic mushrooms and ketamine.

Ketamine was introduced in the 1960s and is still used as an anesthetic by veterinarians as well as many doctors.

It has a broad set of effects on the mind and body, creating a sense of dissociation that can act as a sedative because it changes a person's perception of their self and senses.

This psychological effect made ketamine a popular party drug, starting in the 1980s, and by 1999, the Drug Enforcement Agency (DEA) had classified it as as an illicit substance.

But recent research suggests that, when carefully administered by a professional, ketamine might not provide just temporary 'high' but fast-acting and real relief from depression.

And perhaps relief from often co-occurring conditions, like anxiety and addiction, too.

We don't know exactly why ketamine seems to be so effective for some people with treatment-resistant depression, but 'it does a lot of things throughout the brain and body,' says DrLevine.

'It has a broad spray pattern like a shotgun, so it's probably hitting a lot of those pathways' involved in anxiety and depression, he explains.

At Harvard and Massachusetts General Hospital, researchers gave ketamine infusions to 99 patients. All of them had treatment resistant depression, and about half had high anxiety too.

Though it has mostly been tested for treating patients that only have depression, ketamine worked just as well for patients that had anxiety also.

This, the researchers reported, was 'in contrast to what is observed with traditional antidepressants.'

It isn't clear if the treatment improved anxiety symptoms, however.

Meanwhile, a much smaller study at Yale tested ketamine's effects on addiction.

Ketamine has shown promise for treating addiction, but there has been a significant catch.

Addiction to opioids is one of the toughest to break, plus lethal overdoses are extremely common.

But naltrexone, a common drug used to help treat addiction combat withdrawals, is a bad bedfellow for ketamine, rendering it ineffective, according to a small 2018 study.

More importantly, this made researchers concerned that the reason ketamine seemed to work against depression was that it interacted with the brain's opioid receptors in a way that they had missed previously.

That would make it dangerous for addiction treatment, and would have considerably dulled its clinical promise.

The new Yale study - though done in just five patients - suggests otherwise.

All five had been on naltrexone for a long time, and all five were given ketamine while on it.

The combination treatment proved safe and effective, and the subjects got relief from withdrawal and addiction symptoms as well as depression that was, in part, related to those addictions.

Stanford's previous study was 'a first ever finding, so it should be taken with a grain of salt,' says Dr Levine.

'The new study is exactly proof of that: it's the same design and opposite effect.'

'[The results] raise the possibility that for people who have depression complicated by substance abuse disorders, the combination of ketamine and naltrexone may be a strategy to explore in the effort to optimally treat both condition,' senior study author Dr John Krystal told New Atlas.

Since it is already approved by the FDA, clinics using ketamine off label to experimentally treat depression have already begun to open across the US.

Taken together, the two new studies suggest that we will only see more such treatment centers - and the drug once known for its place in party culture may become a hero for sufferers of complex depression.

'In both cases, we're talking about anxiety and depression and these are two areas and two populations where there is a dire need,' says Dr Levine.

'There's a hopelessness in the in the field, on the part of patients because treatments haven't been particularly effective for managing their symptoms, so these are really hopeful findings.'