Researchers at the University of Alberta said a new study provides a glimpse into how marijuana could affect human embryos.

For a year and a half, they studied the impact of THC and CBD, two chemicals found in marijuana, on zebrafish embryos. Researchers tried several different dosages, comparable to the amounts people use for medicinal or recreational purposes.

The study followed the fish from fertilization to adulthood. It found significant impacts on the physical and mental development of the embryos.

At the highest levels, it even affected survival rates of unhatched embryos.

Researchers caution the results should not be considered proof of how marijuana impacts human embryos.

“I think the research suggests to us that more work needs to be done,”said Declan Ali, one of the study report’s authors and a professor of biological science. “It’s a good starting point to take a look at humans.”

The study has now been published in Scientific Reports, an online journal.