Because more and more Americans, particularly millennials, refuse to buy into antiquated Reefer Madness-like propaganda, marijuana use has more than doubled over the past decade. And because politicians have realized the benefit of making an illegal industry taxable (not to mention the added touch of accurately representing your voter base), marijuana has become much easier to obtain legally.  

Now it seems like almost everyone is using it, including women who are pregnant or nursing. A recent study found that as many as one in twenty women consume cannabis during pregnancy.

And while the long-term effects of marijuana on fetuses and babies remain controversial and poorly understood, medical professionals agree that we should limit exposure as much as possible – because why risk it?  

Unfortunately, we also know very little about how the biologically active compounds in marijuana pass into breast milk. In contrast, there is a wealth of data on how women can avoid exposing their infants to alcohol after drinking. So, what should experts advise to mothers who choose to consume marijuana?

"Pediatricians are often put into a challenging situation when a breastfeeding mother asks about the safety of marijuana use," lead author Christina Chambers said in a statement. "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."

Hoping to provide some answers, Chamber’s team at the University of California San Diego School of Medicine tested 54 breastmilk samples from 50 women who reported using marijuana either daily, weekly, or sporadically. All the new mothers, drawn from a list of donors to a human breast milk repository created to aid scientific research, recalled their exposures to any recreational substances, herbal supplements, and prescription medications for the 14 days prior to milk sample collection and provided additional information on exposures since giving birth.

The results, published in the journal Pediatrics, showed that Tetrahydrocannabinol, aka THC, was detectable in 63 percent of samples, in concentrations ranging from 1.01 to 323.00 nanograms per milliliter. Unsurprisingly, the number of hours since last use and the frequency of use were strongly associated with the concentration. The longest duration between last use of marijuana and measurable THC was about 140 hours (6 days). Though further testing will need to confirm this, the authors estimate that THC has a half-life of roughly 27 hours in breast milk.

Only 9 percent of the samples had measurable concentrations of 11-OH-THC, a metabolite of THC. The same rate was found for measurable levels of cannabidiol (CBD).

Using averages for breastfeeding frequency and breastmilk ingested per session, and assuming the 6 percent bioavailability for THC ingested orally holds true for infants, the authors calculate that infants will end up with blood plasma concentrations of the compound that are roughly 1,000 times less than what the mother’s plasma concentration is. 

"We found that the amount of THC that the infant could potentially ingest from breast milk 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 added. 

Her team is calling for future research into how marijuana might affect children at different stages of development and whether there are differences in exposure between smoked and edible marijuana products.