Breastfeeding mothers should think carefully before lighting up, new research suggests.

The conventional wisdom has been that cannabis use is best avoided during pregnancy and breastfeeding, as there had been little research done on whether THC can be carried by breastmilk to infants. A group of researchers at the University of California San Diego School of Medicine discovered that in many cases it does.

After testing 54 breastmilk samples from 50 women who reported cannabis consumption either daily, weekly or sporadically, the researcher found THC in 63 per cent of the samples. In at least one case, THC was detectable in the milk six days after the mother consumed marijuana.

Christina Chambers, the author of the study warns that while the amount of THC found in breast milk of mothers who consume cannabis is small, the effects of THC on infants is still unknown.

"We found that the amount of THC that the infant could potentially ingest from breastmilk was relatively low, but we still don't know enough about the drug to say whether or not there is a concern for the infant at any dose, or if there is a safe dosing level," Chambers said in a statement.

She says she hopes their research leads to more in-depth studies on the topic and understands that choosing between breastfeeding and medications can often be a challenging choice for mothers.

"Pediatricians are often put into a challenging situation when a breastfeeding mother asks about the safety of marijuana use," Chambers said. "We don't have strong, published data to support advising against use of marijuana while breastfeeding, and if women feel they have to choose, we run the risk of them deciding to stop breastfeeding—something we know is hugely beneficial for both mom and baby."

And while cannabis use and good parenting aren't mutually exclusive, it's probably best to give the weed a break until the kids are onto other foods.

h/t IFLScience