The effects of intranasal oxytocin are not to be sniffed at
When you think about hype in neuroscience, oxytocin is probably one of the first things that comes to mind.
The fanfare surrounding oxytocin has even crept into popular culture. You only need to search ‘oxytocin’ on twitter to see how much this neuropeptide has captured the public’s interest.
Given the hype, it’s no surprise that oxytocin has copped of a fair bit of criticism, both online and within the scientific literature.
In a recent review, Leng and Ludwig outline their own scepticism around intranasal oxytocin. They raise numerous areas where researchers have a poor understanding on how intranasal oxytocin works, which I completely agree with. However, they appear to take this one step further by suggesting that oxytocin’s well-documented cognitive and behavioral effects are suspect because we don’t fully understand the underlying mechanisms.
While a number of excellent points were made in this manuscript, Josh Woolley and myself submitted a recently published comment to Biological Psychiatry (preprint available here), where we remark on a few aspects of their review.
Firstly, the authors assert that there’s widespread publication bias in this field. Now this isn’t uncommon in overhyped research areas but three recent meta-analyses on the effects of intranasal oxytocin reveal no evidence of publication bias. This doesn’t mean that negative oxytocin studies aren’t hiding in a filing cabinet somewhere but it provides fairly strong evidence that the practice of withholding results isn’t commonplace.
Second, they cite one of Josh’s papers as evidence that intranasal oxytocin has no effect on patients with schizophrenia. However, this paper actually reported large effects of intranasal oxytocin on social cognition in the patients (something which has been replicated by others) and subtle effects on healthy participants.
Next, they move onto the issue of oxytocin delivery to the brain. This is a tricky area as we really don’t know much about how intranasally administered oxytocin reaches the brain. Considering the available animal evidence, I’ve proposed how this could occur but we still lack solid evidence of nose-to-brain oxytocin transport in humans.
Notwithstanding these issues, the fact remains that we still (usually) observe social-cognitive effects after intranasal administration — we’re just not really certain how these effects occur.
Finally, we round out our letter by highlighting this:
Research needs to pivot to understanding “how”, “where”, and for “whom” (intranasal oxytocin) works, rather than just simply adding to the growing catalogue of “what” effect this neuropeptide has on cognition and behavior
To be clear, I’m not trying to pretend that intranasal oxytocin is the cure for all that ails psychiatry. Despite this, however, we shouldn’t dismiss its potential simply because we don’t precisely understand how it works.
As Leng and Ludwig write in their reply to us, I hope these kind of open discussions around intranasal oxytocin continue as they will undoubtedly push the field in the right direction.