Birth defects and drug use

• ALSO KNOWN AS: Congenital disabilities and substance abuse; developmental defects and substance abuse

DEFINITION: Congenital anomalies (also called congenital abnormalities, birth defects, or congenital disorders) are problems that develop in the fetus during prenatal development. Congenital anomalies are physical or functional abnormalities present at birth, regardless of cause, which may be genetic, environmental, or of another origin. One of the common preventable causes of congenital anomalies is drug use during pregnancy, including the use of alcohol, tobacco, certain over-the-counter medications, or illicit substances.

Drugs as Teratogens

Teratogens (teratogenic substances) are environmental substances that cause congenital (or developmental) defects. Many teratogenic substances exist, including over-the-counter (OTC) medications, prescription drugs, alcohol, tobacco, and illicit substances.

Most teratogens are most detrimental during the embryonic period (the second to eighth week of pregnancy). It is during this period that organs form. Exposure to teratogenic substances may interfere with critical organ formation. While drugs that are taken between the first and eighth week of pregnancy pose the greatest risk of malformations, exposure to these substances at any point in pregnancy can result in negative repercussions, including intrauterine growth restriction and cognitive or functional problems. Drugs, like most other teratogens, affect the fetus when they cross the placenta along with oxygen and nutrients. High-dose aspirin is one of the over-the-counter (OTC) drugs that is teratogenic, potentially causing bleeding in the mother and fetus.

The use of prescription drugs during pregnancy may be necessary because of a medical condition. If this is the case, medical professionals will prescribe a drug that is not teratogenic or one that is unlikely to harm the fetus. One formerly common prescription drug, the broad-spectrum antibiotic tetracycline, caused discoloration of primary and secondary teeth in utero. In the twenty-first century, another broad-spectrum antibiotic is used to treat infection, decreasing the likelihood of a resultant congenital anomaly.

Generally, when speaking of congenital disabilities and drug use, one commonly attributes defects to tobacco (smoking), alcohol, marijuana, stimulants, sedatives, addictive substances (like heroin or cocaine), and hallucinogens, most of which are teratogenic. Smoking tends to cause heart defects and intrauterine growth retardation. Alcohol exposure most typically causes fetal alcohol spectrum disorder. This condition generally involves stunted growth and other physical, cognitive, and behavioral problems. No definite evidence exists about the teratogenic effects of marijuana, although the drug has been implicated in cases of small head circumference, neurological problems, and learning deficiencies. Investigations are ongoing into the effects of marijuana on prenatal development, especially because marijuana is the single most common drug used by pregnant women. The legalization of medical and recreational marijuana in many states in the United States (US) has brought increased attention to the safety of its use during pregnancy, especially as many pregnant women turn to marijuana for its anti-nausea properties.

Stimulants (including amphetamines) and sedatives (including phenobarbital) can cause developmental defects within the nervous system. Cocaine may cause placental abruptions, causing the deaths of pregnant women and babies, or premature delivery. Opioids like heroin often cause intrauterine growth restriction and cause infants to be born with a physical dependence on these substances, called Neonatal Abstinence Syndrome (NAS). These newborns are at an increased risk of developing a learning disability, sleep disturbances, hyperactivity, developmental delays, and more later in life.

Early research on hallucinogens (like LSD or belladonna) asserted that these drugs could cause chromosomal damage. However, later research refuted this claim.

Many people who use drugs and are pregnant use more than one type of drug. This complicates the situation in that drugs may interact to have a significantly different and greater effect on the fetus.

Drug Treatment During Pregnancy

People who use heroin or other opioids during pregnancy are sometimes treated with methadone. While this is an effective immediate treatment, it does not prevent a fetus from being born physically dependent on the substance. Suboxone (buprenorphine) is a drug used since the 1980s to treat opioid addiction (first used in the US for this purpose in 2002). According to the National Institute on Drug Abuse, the findings of a study published in 2022 suggest that buprenorphine may be a safe and effective alternative to methadone, the standard treatment for opioid dependence during pregnancy. Infants born to people who use heroin, methadone, or Suboxone are commonly evaluated using the Finnegan Neonatal Abstinence Scoring System. This scale helps determine the course of treatment for stopping the use of these substances.

Bibliography

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"Street Drugs and Pregnancy." March of Dimes, Dec. 2024, www.marchofdimes.org/find-support/topics/pregnancy/street-drugs-and-pregnancy. Accessed 22 Oct. 2025.

Suarez, Elizabeth A., et al. "Buprenorphine versus Methadone for Opioid Use Disorder in Pregnancy." The New England Journal of Medicine, vol. 387, no. 22, 2022, pp. 2033-44, doi:10.1056/NEJMoa2203318. Accessed 22 Oct. 2025.

"Substance Use During Pregnancy - Maternal Infant Health." Centers for Disease Control and Pregnancy, 15 May 2024, www.cdc.gov/maternal-infant-health/pregnancy-substance-abuse/index.html. Accessed 22 Oct. 2025.