Shocking images have revealed a little-known, devastating effect of heavy drug use – a condition known as dropped head syndrome.

The pictures – published by doctors at the Al-Zahra University Hospital in Isfahan, Iran – show a 23-year-old man with an extreme bend in his neck, which developed after years of substance abuse.

The drugs caused significant rounding of the spine until the neck could no longer support the head.

Dropped head syndrome – also know as floppy head syndrome – is characterised by severe weakness of the neck muscles, and is most commonly associated with neuromuscular disorders such as motor neurone disease.

But doctors say the syndrome could be caused by substance abuse.

The medics reported that use of amphetamine (also known as speed) triggered what they called a fixed kyphotic neck position, where his chin fell to his chest for long periods.

He also experienced chronic neck pain and paresthesia – the feeling of tingling, numbness, or pins and needles – in his arms.

While the patient had no history of severe neck trauma that could explain his symptoms, he had a history of depression and use of amphetamines, opium and heroin.