After a death in the herd left young Fredzia unable to cope, zookeepers turned to an experimental new treatment they hoped would ease the effects of depression and anxiety in the grieving elephant.

Erna, the largest female and the oldest in the African elephant enclosure at Warsaw Zoo, died in March, leaving behind three grieving younger conspecifics who had to learn their new roles in the fractured group. Fredzia in particular found it difficult to adjust.

This is a major upheaval in any elephant group. Elephants can develop behavioural problems when the structure of a group changes," Dr Agnieszka Czujkowska, who heads the zoo's animal rehabilitation department, told the BBC.

At the time of Erna's death, Fredzia was depressed and showed signs of grief, according to the keepers. The young elephant has since appeared stressed as she has to make friends with her conspecific Buba.

Dr Czujkowska and her colleagues hope that an experimental cannabis oil treatment will alleviate Fredzia's stress and allow the elephant to get along better with the others and restore balance in the herd.

Cannabidiol, known on the market as CBD oil, is extracted from a cannabis plant and is said to increase the production of dopamine and serotonin in the brain, two chemicals known to affect mood. CBD has no psychoactive effects, so the elephants are not intoxicated.

In the experiment in Warsaw, Dr Czujkowska will monitor the elephants' cortisol levels. Cortisol is a hormone produced in the bodies of humans and animals in stressful situations. A control measurement has already been taken.

"We plan to give them the CBD and measure the cortisol again. That's the experiment. Then we will know for sure whether [the oil] works or not," said Dr Czujkowska.

Professor Caitlin O'Connell of Stanford University, who leads the Mushara research project monitoring the social structure of elephant groups, told The Independent that CBD could be a suitable treatment for the Warsaw herd, given the stress-relieving effect it can have on humans, who may not cope with loss as differently as their big-eared peers.

"[Elephants] seem to exhibit similar behaviours to us in the context of loss, and since we have the same hormones, anything that helps reduce anxiety seems worth a try," Professor O'Connell said.

Professor O'Connell writes about the complex ways elephants deal with their grief in her forthcoming book Wild Rituals. In a case not unlike that at Warsaw Zoo, when the matriarch of a herd died, keepers gave younger elephants access to the dead body and two of the deceased animal's closest companions spent all night spreading dirt over the corpse.