While drug addiction in pregnant women can affect fetal development, drug addiction in fathers doesn't normally affect the baby at the time of birth. Addiction can affect sperm quality and development, but these defects usually cause early miscarriage rather than birth defects. Studies have not shown a connection between birth defects and addictive drugs, according to the Organization of Teratology Information Specialists.
The only effect a father can have on prenatal development is at the time of fertilization. Sperm can carry genetic defects related to exposures to certain drugs, but addictive drugs, including alcohol and nicotine, generally have an all-or-nothing effect on sperm, according to Dr. Christina Delos Reyes of Case Western Reserve University. Drugs can cause abnormalities in the sperm that makes it impossible for the sperm to fertilize the egg or for the embryo to develop more than a few weeks before miscarrying.
Several studies have shown a slight connection between certain birth defects, such as certain heart defects, cognitive defects and birth weight, and alcohol use in men, but these connections have not been proven or tested in a large number of studies. Animal studies have shown a more conclusive connection, but more human studies are needed, states Ernest L. Abel, Ph.D., in the June 2004 issue of "Addiction Biology."
Paternal addiction can have a large effect on children after birth. Parental smoking can increase the risk of childhood wheezing, bronchitis and asthma in children, although the connection between asthma was highest in children whose mothers smoked during pregnancy, according to an Austrian study analysis reported in the 2006 issue of "Tobacco Control." Sons of alcohol-addicted fathers have four times the risk of becoming alcoholics themselves, notes the National Association for Children of Alcoholics.
Animal studies have shown more effects from paternal addiction than human studies. It may be that more of a connection exists than has currently been uncovered. Up to 2011, studies have not proven that babies born to addicted fathers exhibit any particular symptoms in most cases unless their mother has the same addiction.