New research from Duke University and Boston University suggests that cannabis use in men may alter sperm DNA in ways that increase the risk of miscarriage and affect early embryo development.

The studies indicate that THC, the main psychoactive compound in cannabis, can trigger epigenetic changes in sperm chemical modifications that influence how genes are switched on or off potentially disrupting critical stages of embryonic growth.

Researchers at Duke University found that regular cannabis exposure alters DNA methylation patterns in sperm, particularly in genes active during the earliest phase of embryonic development. The findings showed that higher levels of THC in the body were associated with more pronounced genetic alterations.

“These changes affect genes involved in growth and development at a very early stage,” one of the researchers said, noting that the impact may emerge days after fertilisation.

Scientists point to a crucial stage known as the maternal-to-zygotic transition, when control of embryonic development shifts from the mother’s genetic material to the father’s. If sperm carries altered genetic instructions, embryo development may stall during this transition.

A separate study by Boston University, which tracked 1,535 couples attempting to conceive, found that men who used cannabis at least once a week were associated with roughly double the risk of miscarriage in their partners, even when the women did not use the substance.

The increased risk was most evident during the first eight weeks of pregnancy, a critical period in which embryonic development is highly sensitive to genetic signals.

The Duke research also identified changes in a gene known as DLGAP2, which plays a role in brain cell communication and has been linked to neurodevelopmental conditions. Experiments in animal models suggested that such changes could be passed to offspring, raising concerns about potential long-term effects.

Researchers say rising cannabis potency may further heighten these risks. Average THC levels have increased significantly over the past decades, with some modern products containing much higher concentrations than in the past.

Based on the findings, scientists advised men planning to conceive to avoid cannabis use for several months to allow sperm to regenerate without potential epigenetic alterations.

While the studies do not establish causation in all cases, the consistent results have prompted calls for greater awareness of how paternal lifestyle choices may influence reproductive outcomes.