Consuming placenta has little benefit for new mothers, according to a study.
The trend of taking placenta capsules after childbirth is growing in popularity in countries such as the UK, France, Germany, Australia and the US.
But researchers found it has little to no effect on the 'baby blues', maternal bonding or fatigue, when compared to taking a placebo pill.
Most experts agree there are many thousands of women in the US alone who carry out the practice, known as maternal placentophagy.
While it appears to be more common in home birth settings, it has been spreading to hospital births, researchers from the University of Nevada, Las Vegas said.
Proponents say that because maternal placentophagy is common in mammals throughout nature, it most likely offers some benefits to human mothers as well.
The new study involved 12 women who took placenta capsules and 15 who took placebo pills in the weeks after giving birth.
Researchers tested the efficacy of placenta capsules in promoting various health benefits, including stemming the onset of postpartum 'baby blues' and depression of new mothers.
The results of the study, published in the online journal Women and Birth, found that such claims are not clearly supported.
However the work did show that ingesting placenta capsules produced small but detectable changes in hormone concentrations that show up in a mother's circulating hormone levels.
Last year, the team released a study showing that consuming encapsulated placentas was not as good of a source of iron as proponents had suggested.
Senior author Professor Daniel Benyshek suggested that both advocates and sceptics alike may point to these new results.
He said: "Placentophagy supporters may point to the fact that we did see evidence that many of the hormones detected in the placenta capsules were modestly elevated in the placenta group mums.
"Similarly for sceptics, our results might be seen as proof that placentophagy doesn't 'really work' because we did not find the type of clear, robust differences in maternal hormone levels or postpartum mood between the placenta group and placebo group that these types of studies are designed to detect."
The study provides no clear evidence of benefits compared to a placebo, which is the scientific standard.
But it does show that the practice is capable of influencing maternal hormone levels and that could provide some kind of therapeutic effect.
To what extent, however, is unclear, and more research is needed in order to explore these effects more fully, the team concluded.
Dr Sharon Young, lead author of the study and programme manager for UNLV's Office of Undergraduate Research, said: "While the study doesn't provide firm support for or against the claims about the benefits of placentophagy, it does shed light on this much debated topic by providing the first results from a clinical trial specifically testing the impact of placenta supplements on postpartum hormones, mood, and energy.
"What we have uncovered are interesting areas for future exploration, such as small impacts on hormone levels for women taking placenta capsules, and small improvements in mood and fatigue in the placenta group."