Researchers say breastfeeding mothers need to know the potential health consequences of marijuana on their babies.

Women who breastfeed their babies and use marijuana should know the drug can stay in their breast milk for almost a week.

A new study last month by researchers from the University of California at San Diego revealed that the drug’s psychoactive component, tetrahydrocannabinol (THC), lingered in breast milk for up to six days.

The findings were published in the journal Pediatrics.

Christina Chambers, PhD, the lead author of the study, says marijuana use is on the rise all over the country. That includes women who are pregnant and breastfeeding.

She told Healthline this type of study is needed because there’s little research on the long-term implications of THC and brain development, particularly in babies.

“It’s a topic of high interest,” she said.

The breast milk tested was from Mommy’s Milk, a human milk research biorepository, headed by Chambers.

The research team plans to conduct further studies that look at a range of issues surrounding breast milk, including nutrient composition and how medications and other substances interact with it.

The samples were donated by mothers who are breastfeeding.

The donations required the mothers to fill out a questionnaire that included inquiries about diet, exercise, mental health, and drug use.

For the study, the team analyzed 54 samples of breast milk for THC. The samples were roughly 2 ounces each. Chambers says they didn’t know how long or how often the mothers used marijuana or how they ingested the drug.

About 63 percent of the samples showed concentrations of THC, but in varying levels. Cannabidiol (CBD) was only detected in about five samples and at a low rate. Chambers says she wasn’t surprised by the findings.

“We expected to be able to detect the THC,” she said. “It accumulates in fat.”

In recent years, the use of marijuana has become more commonplace in society.

A study published last year in the Journal of the American Medical Association found that marijuana use among pregnant women rose from about 4 percent in 2009 to 7 percent by 2016.

Currently, nine states and the District of Columbia allow for the purchase of marijuana for recreational use.

Marijuana carries a so-called “health halo” around it. Meaning, the drug is a natural plant, so people tend to view it void of any negative health risks.

As a result, women who engage in the activity, while pregnant or breastfeeding, tend to believe that the drug isn’t detrimental to the brain development of their developing fetuses or nursing infants.

Dr. Seth Ammerman, a clinical professor of pediatrics and adolescent medicine at Stanford, told Healthline that assumption is false.

Ammerman is on the American Academy of Pediatrics committee for substance use and prevention. He co-authored the committee’s study about the effects of marijuana use during pregnancy and breastfeeding.

He says pregnant and breastfeeding women know that consuming alcohol can cause serious brain development issues. Marijuana consumption should also be viewed in the same manner.

“It’s very likely there could be similar issues with cannabis,” he said.

Ammerman notes that some studies on marijuana were conducted in the 1980s. But back then, the substance’s potency was much less than today, so new research is crucial.

“The marijuana of 30 years ago had a THC concentration rate of 4 percent,” he said. “Today, it’s 15 percent.”

Drs. Maya Bunik and Erica Wymore have also conducted research on marijuana use among pregnant and breastfeeding women.

Both are professors at the University of Colorado. Bunik is a pediatrician and medical director of the Child Health Clinic at Children’s Hospital Colorado. Wymore is a neonatologist at Children’s Hospital Colorado.

Their research, which has yet to be published, showed THC to be present as long as six weeks after use.

They’ve presented their findings at two industry symposiums and are in the process of writing their report for publication in a peer-reviewed journal.

Both doctors say it’s important for physicians to have a conversation with pregnant and breastfeeding women about marijuana use and its potential harm.

Many mothers, they note, are using the drug to cope with depression, stress, or other mental health issues. If that’s the case, then doctors need to first address that.

“Open a conversation, [find out] what are the symptoms are they trying to alleviate,” Bunik said.

Wymore adds that the goal is to promote safe breastfeeding and explain that marijuana isn’t part of that equation. But because of the drug’s growing social acceptance, doctors are challenged to convince women otherwise.

Bunik recalls just the other day a mother was telling her about why she used marijuana.

“She started off the conversation saying, ‘I know you doctors don’t like marijuana,’” Bunik said.

Wymore adds that many people in Colorado assume that because marijuana is now legal to purchase, it’s assumed to be safe.

But in reality, marijuana is still considered an illegal drug at the federal level, she notes, which is why there’s little research to point to the drug’s potential adverse effects.

“The challenge is the difficulty in studying an illegal substance,” Wymore said.