Merck Manual

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Substance Use During Pregnancy


Ravindu Gunatilake

, MD, Valley Perinatal Services;

Avinash S. Patil

, MD, University of Arizona College of Medicine

Reviewed/Revised Nov 2023

Certain substances, including caffeine, aspartame, alcohol, and tobacco, may have harmful effects on pregnant women and fetuses. Illicit drugs include amphetamines, bath salts, cocaine, hallucinogens, cannabis, and opioids (for example, heroin or misuse of prescription opioids).

Use of illicit drugs (particularly opioids) during pregnancy can cause complications during the pregnancy and serious problems in the developing fetus and the newborn. They may result in birth defects, poor fetal growth, or preterm birth. For pregnant women, injecting illicit drugs increases the risk of infections that can affect or be transmitted to the fetus. These infections include hepatitis Overview of Hepatitis Hepatitis is inflammation of the liver. (See also Overview of Acute Viral Hepatitis and Overview of Chronic Hepatitis.) Hepatitis is common throughout the world. Hepatitis can be Acute (short-lived) read more and HIV infection Human Immunodeficiency Virus (HIV) Infection Human immunodeficiency virus (HIV) infection is a viral infection that progressively destroys certain white blood cells and is treated with antiretroviral medications. If untreated, it can cause... read more Human Immunodeficiency Virus (HIV) Infection (including AIDS).

Caffeine Use During Pregnancy

Caffeine, which is contained in coffee, tea, some sodas, or other beverages, chocolate, and some medications, is a stimulant that readily crosses the placenta to the fetus.

It is unclear whether consuming caffeine during pregnancy harms the fetus. Research seems to suggest that consuming caffeine in small amounts (for example, one cup of coffee a day) during pregnancy poses little or no risk to the fetus.

Some experts recommend limiting coffee consumption and drinking decaffeinated beverages when possible.

Aspartame Use During Pregnancy

Aspartame, an artificial sweetener, appears to be safe during pregnancy when it is consumed in small amounts, such as in amounts used in normal portions of artificially sweetened foods and beverages.

Smoking (Tobacco) During Pregnancy

Cigarette smoking Smoking and Other Tobacco Use Tobacco use is a major individual and public health problem. Using tobacco is harmful to almost every organ in the body. Tobacco is used because of the effects of nicotine. Nicotine is highly... read more poses risks to pregnant women and fetuses. Women who are trying to get pregnant or are pregnant should try to quit smoking. Health care professionals can provide resources about smoking cessation programs.

The most consistent effect of smoking on the fetus during pregnancy is

The more a woman smokes during pregnancy, the less the baby is likely to weigh.

Birth defects of the heart, brain, and face are more common among babies of women who smoke cigarettes.

Also, the risk of the following may be increased:

In addition, children of women who smoke have slight but measurable deficiencies in physical growth and in intellectual and behavioral development. These effects are thought to be caused by carbon monoxide and nicotine. Carbon monoxide may reduce the oxygen supply to the body's tissues. Nicotine stimulates the release of hormones that constrict the vessels supplying blood to the uterus and placenta, so that less oxygen and fewer nutrients reach the fetus.

Because of the possible harmful effects of smoking during pregnancy, pregnant women should make every effort to not smoke during pregnancy, including discussing strategies with their doctor.

Pregnant women should avoid exposure to secondhand smoke because it may harm the fetus.

Alcohol Use During Pregnancy

Drinking alcohol Alcohol Use Alcohol (ethanol) is a depressant (it slows down brain and nervous system functioning). Consuming large amounts rapidly or regularly can cause health problems, including organ damage, coma,... read more during pregnancy is the leading known cause of birth defects. Because the amount or pattern of drinking alcohol required to cause fetal alcohol syndrome is unknown, pregnant women are advised to abstain from drinking any alcohol.

Did You Know...

  • The leading known cause of birth defects is drinking alcohol during pregnancy.

The risk of miscarriage Miscarriage A miscarriage is the loss of a fetus before 20 weeks of pregnancy. Miscarriages may occur because of a problem in the fetus (such as a genetic disorder or birth defect) or in the woman (such... read more almost doubles for women who drink alcohol in any form during pregnancy, especially if they drink heavily. Risk is probably related to amount of alcohol consumed, but no amount is known to be risk-free.

Fetal alcohol syndrome is one of the most serious consequences of drinking during pregnancy. Binge drinking as few as 3 drinks a day can cause this syndrome. It occurs in about 2 of 1,000 live births. This syndrome includes the following:

Amphetamines During Pregnancy

Bath Salts (Synthetic Stimulants) During Pregnancy

Cocaine During Pregnancy

Cocaine Cocaine Certain substances, including caffeine, aspartame, alcohol, and tobacco, may have harmful effects on pregnant women and fetuses. Illicit drugs include amphetamines, bath salts, cocaine, hallucinogens... read more taken during pregnancy may cause the blood vessels that carry blood to the uterus and placenta to narrow (constrict). Then, less oxygen and fewer nutrients reach the fetus.

If pregnant women use cocaine regularly, risk of the following is increased:

However, whether cocaine is the cause of those problems is unclear. For example, the cause may be other risk factors that are common in women who use cocaine. Such factors include cigarette smoking, use of other illicit drugs, deficient prenatal care, and poverty.

Hallucinogens During Pregnancy

Cannabis During Pregnancy

The main component of marijuana Marijuana Marijuana (cannabis) is a drug made from the plants Cannabis sativa and Cannabis indica that contain a psychoactive chemical called delta-9-tetrahydrocannabinol (THC). Marijuana... read more (cannabis), tetrahydrocannabinol, can cross the placenta and thus may affect the fetus. No amount of marijuana is considered safe in pregnancy though birth defects are not increased in studies. However, recent studies have suggested that marijuana use in pregnancy may be linked to low birth weight and childhood concerns including attention, learning, and behavioral problems, and changes in brain development and function.

Opioids During Pregnancy

Opioids, such as heroin, methadone, and morphine, readily cross the placenta. Consequently, the fetus may become addicted to them and may have withdrawal symptoms Withdrawal symptoms Opioids, a class of drugs derived from the opium poppy (including synthetic variations), are pain relievers with a high potential for misuse. Opioids are used to relieve pain, but they also... read more 6 hours to 8 days after birth. However, use of opioids rarely results in birth defects.

Use of opioids during pregnancy increases the risk of complications during pregnancy, such as

Babies of heroin users are more likely to be born small.

Drugs Mentioned In This Article

Generic Name Select Brand Names
Cafcit, NoDoz, Stay Awake, Vivarin
Commit, Habitrol, Nicoderm CQ, NICOrelief , Nicorette, Nicotrol, Nicotrol NS
Adzenys, Adzenys XR, Dyanavel XR, Evekeo
Dolophine, Methadose
ARYMO ER, Astramorph PF, Avinza, DepoDur, Duramorph PF, Infumorph, Kadian, MITIGO, MORPHABOND, MS Contin, MSIR, Opium Tincture, Oramorph SR, RMS, Roxanol, Roxanol-T
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