American Health & Medical Research Association
Practical guide

Severe pregnancy vomiting was once blamed on the mind, but a fetal hormone is key

Most pregnant women feel nauseous, and a few develop hyperemesis gravidarum. A hormone from the fetus, and a mother's sensitivity to it, help explain why. This is what eases symptoms and when to get urgent care.

By the Health Research USA editorial team

Published Last updated October 2026

Written from the sources listed below; links checked October 2026. It touches on medicines, doses or health conditions and has not yet been reviewed by a licensed clinician, so use it to prepare for a conversation with yours. How we research and review

Sources15, listed below Reading time15 minutes

Where the evidence stands

  • Strong evidence Antihistamines, including doxylamine with B6, ease symptoms
  • Promising but early GDF15 from the pregnancy, and a mother's sensitivity to it, are central to hyperemesisAcupressure wristbands ease nausea
  • Not enough evidence Ginger treats hyperemesis
  • Evidence says no, or unsafe Severe pregnancy vomiting is mainly psychologicalOndansetron raises overall birth-defect riskCannabis is a safe nausea remedy in pregnancy

Each use is rated separately, from the scorecard in this guide. Safety cautions are spelled out in the guide itself. How we grade

On this page
  1. Doctors once read severe vomiting as a message from the mind
  2. The hormone comes mostly from the baby. The sensitivity comes from the mother
  3. Morning sickness and hyperemesis gravidarum are different problems
  4. Comfort measures help some women. The trials are small
  5. Long vomiting can drain thiamine, and the brain pays
  6. Anti-nausea medicines: a small cleft signal against a serious illness
  7. Cannabis is sold for morning sickness. It can also cause vomiting
  8. The nausea ladder: step up when the basics stop working
  9. Hyperemesis takes an emotional toll. Support helps
  10. Questions readers ask
  11. The bottom line

Key takeaways

  • In December 2023, researchers reported in Nature that GDF15, a hormone made mostly by the fetus and placenta, and a mother’s sensitivity to it each play a large part in who develops severe pregnancy vomiting12.
  • Up to 90% of pregnant women get some nausea, while hyperemesis gravidarum, the severe form, affects about 0.3% to 3.6%4.
  • Weeks of vomiting can drain thiamine, a B vitamin, and cause a brain emergency called Wernicke’s encephalopathy; in 177 published cases, half the pregnancies were lost and 5% of the women died45.
  • Across more than 1.8 million U.S. pregnancies, the anti-nausea drug ondansetron in early pregnancy was tied to about 3 extra oral clefts per 10,000 exposed babies, by our math, and to no rise in heart defects6.
  • Contact your clinician if you can’t keep fluids down for more than 12 hours, feel dizzy or see blood in your vomit; for emotional support, call or text the National Maternal Mental Health Hotline at 1-833-852-626278.

The first author of a 2023 Nature study on pregnancy sickness came to the subject the hard way. Marlena Fejzo, a researcher at the University of Southern California (USC), has described being so sick while pregnant that she could hardly move without vomiting23. In 1999, she lost a baby to hyperemesis gravidarum, the severe form of pregnancy sickness9.

When she went looking for the cause, she found that science had few answers2. For decades, influential medical writers had treated severe vomiting in pregnancy as a sign of hidden emotional conflict10.

In December 2023, Fejzo and a team that included University of Cambridge scientists reported in Nature that a hormone called GDF15 sits near the center of the problem12. The hormone comes mostly from the fetus and placenta, and a mother’s risk depends a great deal on how sensitive she is to it1.

That matters for anyone ever told the illness was in her head.

Doctors once read severe vomiting as a message from the mind

A 2008 review in the journal Current Psychiatry traced how that idea took hold10. Psychoanalytic writers saw pregnancy nausea as unconscious conflict: the sick woman, they suggested, secretly wanted to reject her pregnancy. Some tied the illness to immature or hysterical personalities10.

A 1946 study interviewed 100 women and described 40 of the 57 who had nausea as sexually troubled10. Pushback came in 1973, when Lennane and Lennane argued that the psychological view reflected gender bias, carried forward largely by male authors10.

The 2008 reviewers found that support for a mental cause came from a few poorly designed studies and case reports. Stress, anxiety and depression seemed to follow the vomiting rather than cause it10.

Even in 2023, Cambridge’s announcement called the condition poorly understood and often undertreated2. If you feel brushed off, our article on what to say when a doctor isn’t taking you seriously can help.

The hormone comes mostly from the baby, and the sensitivity comes from the mother

GDF15 acts on the brainstem. Women with more of it in their blood were more likely to vomit in pregnancy and to have hyperemesis gravidarum1.

To learn where the hormone came from, the researchers used a natural variant that made the fetus’s version chemically distinct from the mother’s. More than 95% of the GDF15 in mothers’ blood, and in most cases over 99%, came from the fetus’s genes12.

Women with gene variants, both rare and common, that keep their GDF15 low before pregnancy had a higher risk of hyperemesis13. Women with beta thalassemia, a blood disorder in which GDF15 runs high long term, reported very little nausea or vomiting1.

In mice, the reaction to a dose of GDF15 depended on whether the animals had met the hormone before1. The picture is a body unused to GDF15 meeting a sudden flood of it.

There’s a twist. A mother with a low-GDF15 variant may be less likely to get hyperemesis if her fetus carries it too, USC reported. Those babies were born healthy, the first human sign that lowering the hormone is probably safe3.

The researchers floated ideas: exposing women to the hormone before pregnancy, checking whether metformin, a diabetes drug that raises GDF15, is safe after past hyperemesis, and testing receptor-blocking drugs already in trials for cancer patients3. These were proposals, not treatments. MedlinePlus, the National Library of Medicine’s consumer site, now names GDF15 as the main cause of hyperemesis gravidarum7.

Who paid, and who’s involved. Britain’s Medical Research Council, its National Institute for Health and Care Research and the Wellcome charity were the main funders23. In 2023, Fejzo was research adviser and a board member of the Hyperemesis Education and Research (HER) Foundation, a patient nonprofit, and its executive director was a co-author9. Her team had earlier linked GDF15 gene variants to the condition9.

Morning sickness and hyperemesis gravidarum are different problems

The Royal College of Obstetricians and Gynaecologists (RCOG), the U.K. specialty society, says in its 2024 guideline that nausea and vomiting affect up to 90% of pregnant women, while hyperemesis gravidarum affects 0.3% to 3.6%4. That’s roughly 3 to 36 pregnancies in every 1,000, by our math.

Morning sickness usually starts between weeks 4 and 8 and fades by weeks 16 to 18, MedlinePlus says. Severe vomiting usually eases by weeks 14 to 16, but some women are sick for the whole pregnancy7.

With morning sickness, you can usually still eat and drink some of the time7. Hyperemesis is different in kind. RCOG uses what it calls the Windsor definition4:

  • It starts before 16 weeks.
  • Nausea, vomiting or both are severe.
  • You can’t eat or drink normally.
  • It strongly limits daily activities.

Signs of dehydration support the diagnosis, and rapidly losing 5% or more of your pre-pregnancy weight is a sign of malnutrition4. By our math, that’s 7.5 pounds for someone who weighed 150 pounds.

MedlinePlus adds heavy salivation to the picture7. Risk runs higher with twins or more, a molar pregnancy (abnormal placental tissue), a tendency to motion sickness, HG in a past pregnancy or a female relative who had it7. Clinicians can score severity with validated scoring tools called PUQE and HELP4.

Comfort measures help some women, but the trials are small

RCOG advises eating little and often, avoiding an empty stomach, and resting or taking time off work4. MedlinePlus suggests dry, bland foods such as crackers, and drinking more when nausea is at its lowest. Its list of triggers to dodge includes strong smells, toothpaste, bright lights, car rides and even showers7.

A Cochrane review, from the independent network that pools trial results, covered 37 trials with 5,049 women in its 2014 version11. It found only limited evidence for wristbands that press on an acupressure point inside the wrist called P6, while acupuncture showed no significant benefit11. Ginger, vitamin B6 and anti-nausea drugs also had limited evidence, though the authors stressed that weak evidence isn’t proof a method fails11. A 2015 update exists, but we couldn’t open it.

Our ginger, prenatal vitamin and aromatherapy articles cover those options for milder nausea. One caution belongs here: RCOG says ginger shouldn’t be recommended for hyperemesis gravidarum. In a survey of 512 women, it brought little or no benefit, and 54% reported unpleasant side effects or worse symptoms4.

Long vomiting can drain thiamine, and the brain pays

Thiamine, or vitamin B1, runs low fast when you can’t eat. RCOG warns that stores can run down quickly, with problems possible within about a week of taking in none4.

When they do, Wernicke’s encephalopathy can follow, a potentially fatal brain emergency4. Its signs include blurred or double vision, unsteadiness, confusion or drowsiness, and abnormal eye movements45.

A 2019 systematic review gathered 177 published cases from 146 reports5. Women had vomited for a median of 7 weeks before Wernicke’s set in. Double vision was an early symptom in 37.4% of cases, and blurred vision in 27.4%5.

About 65% of the women had lasting memory or thinking problems, half the pregnancies were lost, and 5% of the women died45. In 63.6% of cases, thiamine doses had been too low, and in 14.1%, glucose given by vein made the condition worse5.

That explains a key RCOG step: anyone admitted to the hospital with vomiting or very low food intake should get thiamine, especially before a sugar drip or IV nutrition4. Case reports capture the worst outcomes, and Wernicke’s is rare. Still, it’s fair to ask about thiamine if you’ve been vomiting for weeks.

Anti-nausea medicines: a small cleft signal against a serious illness

When food changes aren’t enough, RCOG’s 2024 guideline gives its top evidence grade to antihistamines, including doxylamine with pyridoxine (vitamin B6), and a drug family called phenothiazines as first-line treatment4. In the U.S., the American College of Obstetricians and Gynecologists (ACOG) also starts with vitamin B6 and doxylamine, as our prenatal vitamin article explains.

Next comes ondansetron, which RCOG calls safe and effective as a second-line choice4. About 22% of pregnant U.S. women took it at some point in pregnancy in 20146.

In 2018, researchers at Brigham and Women’s Hospital in Boston studied more than 1.8 million Medicaid pregnancies from 2000 to 2013 that ended in a live birth. Of those, 88,467 (4.9%) involved an ondansetron prescription filled in the first trimester6.

Heart defects. The rate was 94.4 per 10,000 exposed babies versus 84.4 per 10,000 unexposed. After adjusting for other ways the two groups differed, the researchers found essentially no difference (adjusted relative risk 0.99), and no rise in birth defects overall6.

Oral clefts. The rate was 14.0 per 10,000 exposed babies versus 11.1 per 10,000 unexposed6. By our math, that’s about 3 extra clefts for every 10,000 exposed babies, or roughly 1 extra for every 3,400. The authors said a small increase couldn’t be ruled out6.

RCOG says that small risk should be weighed against poorly controlled vomiting4. Regulators split: the European Medicines Agency advised avoiding ondansetron in the first trimester, while the U.K.’s medicines regulator did not4. NIH grants funded the Boston study, and some co-authors reported drug-company funding for other work6.

Untreated hyperemesis carries risks, too. RCOG advises trying every treatment before ending a pregnancy is considered4. A pooled analysis of 19 studies found a small rise in problems among children of women with HG, from weak and varied evidence4. Medicine choices belong to you and your prenatal clinician, so bring these absolute numbers to that talk.

Cannabis is sold for morning sickness, and it can also cause vomiting

In a 2018 study, a caller posing as a woman 8 weeks pregnant with morning sickness phoned 400 randomly chosen Colorado dispensaries12. Of them, 69% recommended cannabis, rising to 83% among dispensaries with medical licenses. The release said 65% based their advice on personal opinion, and fewer than a third of staff urged the caller to talk with a doctor first12.

The FDA strongly advises pregnant people to avoid THC, CBD and marijuana in any form. It cites links between marijuana in pregnancy and lower birth weight, premature birth and effects on the developing brain13. The American College of Obstetricians and Gynecologists and the U.S. Surgeon General also advise against use14.

Many people see cannabis as a natural nausea remedy, a 2023 paper in AJOG Global Reports noted14. Yet cannabis can cause or worsen severe, recurring vomiting, a pattern called cannabinoid hyperemesis syndrome, which may be more common than doctors realize14.

It can look just like hyperemesis gravidarum. In a 2018 case report, a pregnant 20-year-old kept landing back in the hospital with nausea and vomiting, and staff noticed her frequent hot showers15. With no other cause found, doctors diagnosed the cannabis syndrome and treated her with anti-nausea medicine and abstinence15. The authors suspect it’s often missed in pregnancy15.

If cannabis has helped you get through the day, telling your clinician isn’t a confession; it helps them tell one vomiting illness from another. Our companion article on pregnancy supplement risks covers cannabis and babies.

The nausea ladder: step up when the basics stop working

This ladder is our own summary of RCOG and MedlinePlus advice. Climb it with your clinician.

Rung What it involves Move up when
1. Food and routine Little and often, bland foods, fewer triggers, rest47 You can’t keep up with fluids, food or daily tasks47
2. Comfort add-ons Wristbands, ginger or scents for milder nausea711 Nausea still limits eating, or ginger makes you feel worse4
3. First-line medicine Antihistamines, including doxylamine with vitamin B64 Symptoms persist4
4. Second-line medicine Ondansetron or other options, weighing the small cleft signal46 Treatment at home isn’t working4
5. Day-unit care IV fluids and anti-nausea medicine as an outpatient47 You can’t keep pills down, or you’re dehydrated or down more than 5% of your weight despite treatment4
6. Hospital care Fluids, thiamine before any sugar drip, IV or tube feeding if needed47 Your team plans next steps with you

How strong is the evidence?

Claim Rating What it rests on
GDF15 from the pregnancy, and a mother’s sensitivity to it, are central to hyperemesis Promising but early One landmark study whose genetic, blood and lab findings point the same way, building on the team’s earlier gene work; not yet tested as a treatment target129
Severe pregnancy vomiting is mainly psychological Evidence says no, or unsafe Old theories built on weak studies10
Acupressure wristbands ease nausea Promising but early Limited evidence in a Cochrane review11
Ginger treats hyperemesis Not enough evidence No trials in severe cases; a survey found little benefit4
Antihistamines, including doxylamine with B6, ease symptoms Strong evidence RCOG’s highest grade4
Ondansetron raises overall birth-defect risk Evidence says no, or unsafe No overall or heart-defect rise; about 3 extra clefts per 10,00046
Cannabis is a safe nausea remedy in pregnancy Evidence says no, or unsafe FDA advises against it, and it can cause vomiting131415

Hyperemesis takes an emotional toll, and support helps

RCOG cites a U.K. survey of 5,071 people affected by the condition. A quarter had occasional thoughts of suicide, 6.6% regularly considered it, and 52.1% considered ending the pregnancy4.

About 1 in 10 women with HG ends a wanted pregnancy because of it, RCOG says, and the illness is a risk factor for post-traumatic stress after birth4. MedlinePlus adds that anxiety and depression may last beyond pregnancy7. None of that is weakness.

The federal National Maternal Mental Health Hotline is free, confidential and open 24 hours a day8. Call or text 1-833-852-6262 (1-833-TLC-MAMA). Counselors answer in English and Spanish, with interpreters for about 60 other languages8.

It isn’t a crisis line: for thoughts of suicide, call or text 988, and for immediate danger, call 9118. RCOG also points patients to peer support from the HER Foundation and the U.K. charity Pregnancy Sickness Support4.

Natural-health values fit this story well. Listening to your body, insisting on being heard and asking how a remedy was tested pushed this research forward. Food, rest and comfort come first on the ladder. But when you can’t keep food down, even thiamine has to come another way, and that’s no failure of natural care.

Questions readers ask

Will hyperemesis come back in my next pregnancy?

It often does. Studies reviewed by RCOG found recurrence rates from 15% to 81%, and 89% in a self-reported survey4. Talking with your clinician before your next pregnancy can help you plan early care.

My urine test showed ketones. Does that mean I’m dehydrated?

Not necessarily. RCOG’s 2024 guideline says ketones in urine aren’t a reliable sign of dehydration, a recommendation with its top evidence grade4. Your team will also look at your pulse, blood pressure, blood tests and weight7.

Is CBD safer than marijuana in pregnancy?

The FDA advises against CBD, THC and marijuana in any form during pregnancy13. Our companion article on the rest of the pregnancy shelf explains why CBD isn’t a gentler loophole.

The bottom line

Severe pregnancy vomiting isn’t a weakness or a state of mind. A hormone made mostly by the fetus, meeting a mother whose body isn’t used to it, appears to explain much of who gets dangerously ill, and it points toward future treatments.

For now, start with food, rest and fewer triggers, and move up the ladder without guilt. Antihistamines have strong evidence, ondansetron’s cleft signal is small in absolute terms, and thiamine protects the brain when vomiting drags on. Get care fast for dehydration, blood in your vomit or vision changes.

Keep exploring: pregnancy nutrition and vitamin A pregnancy birth defects.

About this article

This article was researched using a peer-reviewed genetic study and university releases about it, a 2024 U.K. clinical guideline, NIH’s MedlinePlus, a Cochrane review, a large U.S. drug-safety study, a systematic review, published case reports, an FDA consumer update and federal hotline pages, all listed below. It was reviewed in October 2026. It is general education, not medical, legal or financial advice.

Sources

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  2. University of Cambridge, Cambridge Reproduction. News item on the Nature GDF15 study. December 13, 2023. repro.cam.ac.uk
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  12. Denver Health. “Study Finds Marijuana Dispensaries Are Recommending Smoking Pot While Pregnant for Morning Sickness.” News release, May 9, 2018, on Dickson B, et al., Obstetrics & Gynecology, 2018. denverhealth.org
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  14. Galvin SL, Coulson CC. “Addressing cannabis consumption among patients with hyperemesis gravidarum.” AJOG Global Reports, 2023;3(2):100180 (abstract via DOAJ). pubmed.ncbi.nlm.nih.gov
  15. Kim HG, Moon J, Dixon H, Tullar P. “Recurrent Nausea and Vomiting in a Pregnant Woman with Chronic Marijuana Use.” Case Reports in Obstetrics and Gynecology, 2018 (abstract via DOAJ). pubmed.ncbi.nlm.nih.gov