Unfriendlier due to serotonin

Serotonin is known as the ‘happy hormone’, but it can also make you less friendly, according to new research findings.

It was a surprising outcome, says doctoral candidate Koen Hogenelst who has studied the effects of serotonin on social behavior in depth. You would expect people to become friendlier and more social with a higher level of serotonin in their brains, but that is not always the case.

Serotonin is a neural transmitter which transmits messages to several areas in the brain. ‘It plays an important role in the processing of emotional and social information’, says Hogenelst.


In people who have depression, there is often something wrong with this neurotransmitter. In those cases, the people are extremely somber and retreat into themselves. This is why anti-depressants often try to influence the serotonin level in the brain. The fact that this often has positive effects on their mood is clear, but what does it do to their social behavior?

In order to research this, Hogenelst gave test subjects tryptophan, a harmless amino acid which is converted into serotonin in our brains. The other test group received a placebo. Just as expected, the test subjects who took the tryptophan felt happier than those who took the placebo. However – and this was not expected – they became less friendly. ‘They were quicker to confront each other about things that bothered them and were more often critical. They were also slower to agree with others.’


Does that mean that serotonin makes you happier, but also meaner at the same time? ‘No’, says Hogenelst. ‘I think it has something to do with standing up for yourself. My test subjects were people at high risk for depression, as it runs in the family. It is possible that they already have difficulty with this. The serotonin thus helps them to be more assertive and say: I want this, or I don’t.’