Writing in the journal Current Biology, researchers at Johns Hopkins University in the US said the drug affected octopus in a manner similar to humans.
Under normal circumstances, octopuses are solitary animals that can prey on one another after mating.
Researchers say the way they behave while using drugs can provide insight into how social behavior has evolved.
MDMA (methylenedioxy-methylamphetamine), also known as ecstasy, is a powerful drug for changing moods that flood the human brain with chemicals called serotonin.
Serotonin makes people more sociable.
Although octopuses are intelligent creatures, their brains are physically very different from humans. For this reason, researchers are not sure how they will respond.
What did the research show?
Gl Dlen, a neurologist at the Johns Hopkins University School of Medicine who led the study, designed an experiment with three connected underwater rooms. One of them contained trapped octopus, and the other was a plastic toy.
Four other octopuses were placed in a tank to test their reactions. The researchers measured how long they spent with other animals, and how long they took with toys.
Then, they will be given MDMA liquid, which is absorbed through the gills, and placed in a room again.
This study found that all four spent more time with other octopuses than before being given drugs.
“They tend to hug the cage and put their mouths in the cage,” said Prof. Dlen.
“This is very similar to how humans react to MDMA; they often touch each other,” he said.
What does this research mean?
The findings suggest brain chemicals may be a key social behavior of various very different species. This is true even though many nerve cells react to serotonin in the hands of an octopus.
“We can say the octopus brain is completely different from humans, but we need these synapses or neurotransmitters,” said Prof. Dlen. “We can write a list of the minimum builders of this complex behavior.”
Maybe not an impressive brain circuit that supports social behavior, but basic signal chemicals.
Other researchers have asked questions about research methodology, but Professor Harriet de Wit of the University of Chicago, who has studied how ecstasy affects animals, says it is “innovative and interesting” – but we cannot be sure that it is entirely due to the drugs.
Ideally, the experiment will be repeated on a larger scale, approved by the researchers.
And some octopuses will be placed in the tank for the first time after absorbing ecstasy, and others will not.
Prof. de Wit said that would help rule out the idea that they were more friendly in the second trial because they were used to tanks, or other octopuses.