marijuana links to learning disabilities
Marijuana Exposure During Pregnancy

Links to Learning Disabilities, ADD and Behavior Disorders

The following is one chapter from a 1997 Graduate Student Research Project conducted at the
University of South Florida.  The project involved locating published peer reviewed medical journal articles which have shown various environmental and chemical exposure factors can cause learning disabilities, hyperactivity and other disorders by damaging the delicate brain growth process in the unborn child during pregnancy.

Author: Richard W. Pressinger (M.Ed.)
Project Supervisor:
Kofi Marfo (Ph.D.) University of South Florida, Special Education Department
email correspondence:
Learning Disability Research Web Site:



About 25% of Americans 18 to 25 years of age used marijuana to some degree according to 1980 figures from the Department of Health, Education & Welfare. Recent studies also indicate considerable marijuana use among pregnant women as well. In a study at Carleton University, Canada,by Dr. P. A. Fried, of 420 predominantly middle class Canadian pregnant women, approximately 18% of young women admitted to using marijuana to some degree before becoming pregnant, 13% were irregular users, 2% were moderate users and 3% admitted heavy use (1).

The most frequent age of marijuana use for women is also the age of childbearing. Fifty percent of 18-35 year old women reported using marijuana at least once, and 8% reported using marijuana a minimum of 10 out of the past 30 days (Clayton, R. R., Voss, H. L., Gender differences in drug use: An epidemiological perspective. In: Ray, B.; Braude, Ml, eds. Women and drugs: A new era for research. NIDA Res. Monogr. 65:80-99, 1986.)

However, lower socioeconomic status appears to have a significant effect on marijuana usage in women. In a 1983 random sample of 1360 women interviewed from an inner-city prenatal clinic in the Pittsburgh area, 36% of the women were moderate or heavy marijuana users (3 or more joints/day) before becoming pregnant. After becoming pregnant the rate dropped to 25% by the first trimester.

Heavy marijuana use (one or more joints/day) during the first month of pregnancy averaged 20% for the first trimester but decreased to 7% for the second and third trimester in this same group. Women who used marijuana heavily during the first trimester of pregnancy did not differ from women who abstained throughout pregnancy in terms of age and education, however, they were more likely to be black and unmarried. They also had a lower income and reported more substance use during pregnancy, including alcohol, tobacco and illicit drugs other than marijuana

Regarding "any" marijuana usage before pregnancy in this sample of 1360 women, 44% reported marijuana use. This is compared to a rate of 22% reported in a general population sample by the National Institute on Drug Abuse in the 1988 national household survey on drug abuse.

The main psychoactive ingredient in marijuana, THC, crosses the placenta and has the potential for harming pregnancy outcome. Some recent epidemiological studies suggest that maternal marijuana use during pregnancy may result in perinatal hypoxia (low oxygen to the baby), premature labor, low birthweight and physical and behavior anomalies in the offspring. However, marijuana use has been difficult to measure in these reports, since it is an illegal drug, and therefore prone to under-reporting, and many of the women studied also used other drugs, raising the possibility of drug interactions with marijuana.


Marijuana Use Increases Symptoms of
Attention Deficit Disorder in First Grade Children

SOURCE: Neurotoxicology and Teratology, 14:299-311, 1992

Six year old children are more likely to show signs of Attention Deficit Disorders if their mothers smoked 6 or more marijuana cigarettes per week. This was the conclusion after testing 126 children at the Department of Psychology, Carleton University, Canada. Fourteen of the children had mothers who admitted smoking between 1 and 6 "joints" per week and 19 had mothers who admitted smoking at least 6 marijuana joints per week during pregnancy.

The testing was done using the Gordon Vigilance Task to examine "sustained attention." A series of single-digit numbers were shown on the computer screen at a rate of 1 per second. Each subject was asked to press a button whenever the number "1" appeared after the number "9" on the video screen. The children of heavy marijuana smokers made more errors of "omission" in which they forgot to press the button when the "1" appeared after the number "9".

Although the results were not as strong as for those children whose mothers smoked cigarettes, the researchers stated in conclusion,

"The data pertaining to maternal use of marijuana, are suggestive of an association between that drug and particular aspects of attentional behavior - possibly sustained attention. Cognitive psychologists have frequently divided the attentional process into three sub-systems that perform different but interrelated functions. These include orienting toward sensory events, detecting signals to be focused on including information stored in memory and maintaining a vigilant state." The present findings suggest that prenatal exposure to cigarettes and marijuana may be associated differentially with subsystems within the attentional process....In addition, Discriminant Function Analysis revealed a dose-response relationship between prenatal marijuana use and a higher rating by the mothers on an impulsive/hyperactive scale."

Dr. Peter A. Fried, Barbara Watkinson
Department. of Psychology, Carleton University, Ontario, Canada
A Follow-up Study of Attentional Behavior in Children
Exposed Prenatally to Marijuana, Cigarettes, and Alcohol
Neurotoxicology and Teratology, 14:299-311, 1992


Combining Alcohol & Marijuana
Increases Miscarriage

SOURCE: Teratology 31:35-40 (1985)

If this animal research carries over even slightly to humans, there is another reason to add for the fertility and miscarriage problems being experienced by some of today's couples. In a study at the Research Institute on Alcoholism, Buffalo, New York, Dr. Ernest L. Abel tested the hypotheses that alcohol in combination with marijuana would decrease fertility far more than if either drug was used alone. Using both rats and mice, Dr. Abel exposed 85 of the animals to either alcohol or marijuana, or alcohol plus marijuana, along with a control group that was not exposed. Exposure levels of the drug were determined from previous research as the maximum level that did not cause any reproductive problems.

The results showed that neither alcohol or marijuana used alone caused any significant increases in resorptions or fetal deaths, however, when alcohol and marijuana were used in combination, there was a 73% fetomortality (offspring deaths) in rats and 100% fetomortality in mice.

Dr. Ernest L. Abel, Research Institute on Alcoholism, Buffalo, New York
Alcohol Enhancement of Marijuana-Induced Fetotoxicity
Teratology 31:35-40 (1985)

Additional References

  1. Neurobehavioral Toxicology and Teratology, 4:451-454,1982,
    Department of Psychology, Carleton University, Ottawa Canada. Dr. P.A. Fried