It's been revealed three soldiers were sent home from Afghanistan earlier this year for misusing controlled drugs.

The soldiers had been using Penthrox, a morphine-type painkiller that is inhaled.

Defence Force spokesman Major John Gordon said an investigation was commenced as soon as the issue came to light.

He said the soldiers were disciplined in Bamyan province under military law then sent home as soon as they were found guilty.

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Major Gordon said they were sentenced to 28 days in military prison at Burnham Military Camp, south west of Christchurch.

They were also fined $1500 each.

Major Gordon said their employment would've been reviewed but they're still working at the Defence Force.