DURHAM, N.C. (WTVD) -- A new study shows that a dad's drug use may have a huge effect on his baby's development.Dr. Theodore Slotkin, PhD., a professor in pharmacology and cancer biology at Duke University, said he has been studying the effects of chemicals on child brain development for decades."My entire career has been dedicated to finding out what environmental factors affect development," Slotkin said.But, he said, most of the previous research has focused on maternal habits, rather than what dads do before pregnancy."For decades, people have been studying all the things that mom shouldn't do," Slotkin said in a phone interview. "The guys have been getting a free pass."In the study, published in the journal Toxological Sciences, Slotkin and his team injected male rats with varying amounts of tetrahydrocannabiol (THC) daily for about a month before mating them with female rats that had not been exposed to drugs. Slotkin said the amount of THC injected would be comparable to moderate daily use in an adult human.Slotkin said his team injected the THC rather than giving it to them to eat or exposing them via smoke because rats metabolize THC much more quickly than humans and his team wanted to make sure that all of the rat's sperm were exposed to THC.Slotkin said his study shows that changes in the father's sperm could affect how their offspring's brains develop in the womb. He said the sperm undergoes what are known as epigenetic changes--basically, genes that would normally be turned on during brain development are switched off. Once the rats were born, the researchers saw decreased communication between brain cells in the pups' whose fathers were exposed to the highest amount of THC, similar to the kind of reduced brain activity seen in Alzheimer's disease. Slotkin's team and observed deficits in learning, memory and attention in these rats.In the study, Slotkin and the other authors wrote that the extent of the activity deficit was comparable to those seen with direct fetal exposure to pesticides, nicotine or tobacco smoke from the mother during pregnancy.Though this study used rats as a model organism, Slotkin said the takeaways from the study can be translated to human men."Epigenetic changes in human sperm resemble the same changes in rat sperm," Slotkin said.While more studies would need to be done to come to any kind of conclusion about the effects of paternal marijuana use, Slotkin said the research should give users pause as more states legalize marijuana and cannbidiol (CBD) products and both direct and indirect exposure to all of the compounds in marijuana increases.Slotkin, who earlier in his research career showed the effects of nicotine and neurotoxins found in pesticides on early brain development, said, "This has been a lifelong quest to make kids' lives better."In the paper, the team wrote that the research was funded by the John Templeton Foundation , an organization that aims to support research at the intersection of religion and science.Next, Slotkin hopes to compare the effects of paternal THC intake on brain development to use of other chemicals found in marijuana smoke, like CBD.