A four-month-old baby was left "clinically dead" after his drug-addicted parents gave him crystal meth to stop him from crying.

Slovakian husband and wife Silvia Strnadova, 26, and Miroslav, 30, took their unconscious child to hospital where they demanded to see a doctor.

But the child was already brain dead and is now only being kept alive by a life support machine, said Anna Moracikiva, the hospital's head doctor.

"The child's brain is severely damaged and he is clinically dead. His chances of survival are minimal and he is being kept alive by a life support machine," she said.

Miroslav 'the Crocodile' and Silvia Strnadova (Supplied). (Supplied)

Police arrested the couple after doctors discovered the infant had been given a strong dose of methamphetamine.

Neighbours were shocked when they heard the news about the couple but admitted the couple had a notorious reputation in the town of Prievidza, in the north west of the European nation.

"Really weird people kept going to their apartment. I always worried about letting my children play outside because you never knew what would happen," neighbour Jana Trznikova said.

Ms Trznikova said Miroslav was known as the "Crocodile" due to his dangerous short temper and because he had "a reputation for being the best crystal meth cooker".

A police spokesman said the father admitted to giving the baby meth to stop it crying and was arrested for neglect and causing harm to the child.

"That may change if the child dies," the spokesman said.

"He is in custody, while the woman has for the time being been released."

The mother, who has two more children to two different fathers, is being investigated for failing to protect the infant.