Marijuana is more widely available than ever, but what does it do to babies?

There’s no answer to that yet, but nursing mothers are being warned to avoid it: Traces of the drug can show up in breast milk, according to the American Academy of Pediatrics.

Tetrahydrocannabinol, or THC, the psychoactive ingredient in marijuana that gets people high, can be detected in breast milk up to six days after use of the drug, according to a study published on Monday by the journal Pediatrics.

The study found that tetrahydrocannabinol was detectable in 63 percent of 54 samples of breast milk from women who said they had used marijuana before pumping.

In response to evidence that babies are being exposed to marijuana, the A.A.P. recommends that women avoid the drug altogether when they are pregnant or breast-feeding.