Australian Defence Force (ADF) personnel are being treated in secret for post-traumatic stress disorder (PTSD) and other mental health conditions to avoid jeopardising their careers, according to serving and former members.

Key points: ADF members say they speak to mental health professionals outside the Department

ADF members say they speak to mental health professionals outside the Department Talking about mental illness could jeopardise worker's career, members say

Talking about mental illness could jeopardise worker's career, members say ADF says reporting mental illness ensures members are provided with proper support

James (not his real name) has just recently retired from a 25-year career in the Australian Army and said he never told the ADF he had PTSD.

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"I'd go and speak to professionals outside of Defence," he said.

"I'd go see a psychologist and talk to them about what was wrong."

The ADF told the ABC in a statement that members were required to tell them if they were being treated outside the ADF system.

But James said if he spoke up about his mental illness, he risked his career.

"There are lots and lots of guys and women who get treatment outside of Defence because as soon as you put your hand up and say there is something wrong ... you get treated completely differently," he said.

"You're almost alienated from the system ... you can't go to work, you can't drive a vehicle, can't carry a weapon."

Serving member Mark (not his real name) told the ABC he was being treated for depression, also outside the system without the ADF knowing.

"It is to protect my career, by bringing it up it would hinder any further career [opportunities]. It is career suicide," Mark said.

Another serving member Scott (not his real name) said his case showed what could happen when you were honest about your symptoms.

He said he was downgraded to a non-deployable status after revealing during a mandatory post-deployment debrief that he had recurring dreams.

"When we get home, if we're having nightmares and the like, which is the body's natural reaction to this trauma, we should [be] able to talk about it without it becoming career suicide," he said.

Scott believed some soldiers could continue in their roles with mental health conditions.

"People have a lot of individual coping mechanisms, they're still good at their job, they're great at their job," he said.

"But if you were to present with three different things that ultimately tick the boxes for PTSD, you're diagnosed and you're no longer deployable for that period of time until you can get an upgrade."

Stressful situations 'likely to exacerbate symptoms'

In a statement, the ADF said some members who present with mental health conditions may have their deployable status reclassified while undergoing treatment.

It said that was to ensure members were provided with proper support and the opportunity to recover.

Psychologist Melissa Harries worked for the ADF for about 10 years, and said it was upholding its duty of care.

"Someone who has post-traumatic stress disorder for example, and they are currently experiencing symptoms, if we put that person under stress or pressure or expose them to further trauma, then that's likely to exacerbate their symptoms," Ms Harries said.

She said she was aware of people being treated in secret outside of the ADF.

"I actually think that's okay," Ms Harries said.

"It's not desirable but I'd rather those people be accessing support regardless of where it comes from."