Is flaxseed safe during pregnancy?

Nobody can say for sure, because we found no randomized trial of whole or ground flaxseed in pregnant women. The closest large body of evidence is about its omega-3. A 2016 US government systematic review of 95 randomized trials found that alpha-linolenic acid (ALA) supplements in pregnancy did not change birth weight, and its authors rated that evidence low strength. The NIH National Center for Complementary and Integrative Health (NCCIH) says some studies suggest flaxseed is possibly unsafe in pregnancy, and that the evidence is not conclusive.

Unsettled. This is a question with almost no direct data. The safety warning comes from an agency page that does not name its studies, and the trials that exist tested flaxseed oil capsules with vitamin E in 60 women with gestational diabetes. We found no study of ground or whole seed eaten as food in pregnancy, for harm or for benefit.

What the trials found

The 2016 review for the Agency for Healthcare Research and Quality covered 95 randomized trials and 48 observational studies of omega-3 in pregnancy and breastfeeding. EPA plus DHA or ALA supplements had no effect on birth weight, on low strength of evidence. Few of the trials tested ALA at all, most tested DHA or fish oil, and none tested flaxseed as a food.

A 2020 meta-analysis of 14 comparisons found omega-3 supplements lowered the risk of preeclampsia, with a relative risk of 0.82 (95% CI 0.70 to 0.97). Pregnancy-induced hypertension did not change, at 0.98 (0.90 to 1.07) across 10 comparisons. The pooled trials were mainly fish oil, the abstract does not report ALA arms separately, and it does not give absolute risks. So the result cannot be credited to flaxseed.

Two reports from one randomized trial in Iran are the only ones in pregnant women that used flaxseed oil. Sixty women with gestational diabetes took capsules of 1000 mg omega-3 from flaxseed oil together with 400 IU vitamin E, or placebo, for 6 weeks. Fasting glucose fell by 11.8 mg/dL on the supplement and rose by 1.5 mg/dL on placebo. Their newborns had jaundice less often, 10.3% against 33.3%. Both results come from one small center, the vitamin E means the flaxseed oil effect is not isolated, and a sister paper from the same group later received an expression of concern from its journal.

In a US cohort of 321 pregnant women, higher plasma ALA in the first trimester was linked with larger fetal size and weight through the rest of pregnancy. This is an association with a blood marker. Plasma ALA comes from many foods, and the study recorded no flaxseed intake.

Who should be careful

The caution is from NCCIH: some studies suggest flaxseed is possibly unsafe in pregnancy, and the evidence is not conclusive. The page does not name the studies. One possible source is a 2010 letter on herbal products and preterm birth in a Quebec pregnancy registry, which we could not read, so we report no figure from it.

For breastfeeding, NCCIH says little is known about whether flaxseed is safe. NCCIH also says there are theoretical reasons flaxseed or its oil might interact with anticoagulant or antiplatelet drugs. No clinical cases are cited for that. It matters in pregnancy because low-dose aspirin is often prescribed to prevent preeclampsia.

Not for everyone. The NCCIH caution covers flaxseed in pregnancy without separating seed, oil and supplements, and nothing we found shows any of them to be safe. If you take aspirin or another blood thinner, raise flaxseed with the person treating you before you start it.

What expert bodies say

NCCIH, part of the US National Institutes of Health, is the only body position we found. In its February 2025 fact sheet it calls flaxseed possibly unsafe in pregnancy on inconclusive evidence, unknown in breastfeeding, and a theoretical concern alongside blood thinners. The LactMed drugs and lactation database had no flaxseed record that we could reach.

How we searched

What would change this answer

• A cohort that records flaxseed eaten as food, apart from oil and supplements, and follows women to preterm birth and birth weight. ClinicalTrials.gov lists no registered trial of flaxseed in pregnancy.
• A trial of ground flaxseed for constipation in pregnancy that measures safety outcomes.
• The Quebec preterm finding published in full, so the agency caution can be weighed on its data.

Nutrition facts and the cholesterol evidence for the seed itself are on the flaxseed page.

Sources

1. ev-flpr-01 · Meta-analysis or systematic review · systematic review of RCTs and prospective observational studies (AHRQ Evidence Report) · n = 95 RCTs and 48 observational studies
   Prenatal EPA plus DHA or alpha-linolenic acid (ALA) supplementation had no effect on birth weight (low SoE).
   
   Who: pregnant or breastfeeding women and neonates in RCTs of omega-3 fatty acids, 2000 to August 2015
   Effect: ALA supplementation: no effect on birth weight (low strength of evidence); DHA raised birth weight and gestation length slightly (moderate)
   Certainty: Few ALA arms; most trials tested DHA or fish oil. No trial of whole or ground flaxseed food identified.
   Evid Rep Technol Assess (Full Rep), 2016 · checked 2026-10-07 · we read the abstract
2. ev-flpr-02 · Meta-analysis or systematic review · systematic review and meta-analysis of clinical trials · n = 14 comparisons
   The meta-analysis of the 14 comparisons demonstrated that n-3 fatty acids supplementation played a protective role against the risk of preeclampsia (RR, 0.82; 95% CI, 0.70-0.97; p = 0.024; I2 = 19.0%).
   
   Who: pregnant women in clinical trials of EPA, DHA and/or ALA supplementation, 1991 to 2018
   Effect: preeclampsia RR 0.82 (95% CI 0.70 to 0.97), I2 19%; pregnancy-induced hypertension RR 0.98 (0.90 to 1.07), 10 comparisons
   Certainty: Pools mainly marine omega-3 trials; ALA-only or flaxseed arms not separated in the abstract, so the effect cannot be attributed to flaxseed.
   Taiwan J Obstet Gynecol, 2020 · checked 2026-10-07 · we read the abstract
3. ev-flpr-03 · Randomized controlled trial(s) · randomized, double-blind, placebo-controlled trial, 6 weeks · n = 60
   Patients were randomly allocated to take either 1000-mg omega-3 fatty acids from flaxseed oil plus 400-IU vitamin E supplements (n = 30) or placebo (n = 30) for 6 weeks. … After 6 weeks of intervention, changes in fasting plasma glucose (-11.8 ± 11.0 vs +1.5 ± 11.9 mg/dL, P < .001), serum insulin concentrations (-1.8 ± 6.9 vs +5.8 ± 12.1 μIU/mL, P = .004), homeostasis model of assessment-estimated insulin resistance (-0.8 ± 1.6 vs +1.4 ± 2.8, P = .001), homeostasis model of assessment-estimated beta cell function (-0.2 ± 27.7 vs +22.8 ± 48.2, P = .02), and quantitative insulin sensitivity check index (+0.01 ± 0.02 vs -0.01 ± 0.02, P = .01) in the omega-3 fatty acids plus vitamin E group were significantly different from the changes in these indicators in the placebo group.
   
   Who: women with gestational diabetes not taking oral hypoglycemic agents
   Effect: fasting plasma glucose -11.8 vs +1.5 mg/dL (P < .001); HOMA-IR -0.8 vs +1.4; triglycerides +10.8 vs +34.2 mg/dL; no effect on total or LDL cholesterol after adjustment
   Certainty: Single-center Iranian trial from a group with a later expression of concern on a sister paper (31902378); co-supplemented with vitamin E, so the flaxseed oil effect is not isolated.
   J Clin Lipidol, 2016 · checked 2026-10-07 · we read the abstract
4. ev-flpr-04 · Randomized controlled trial(s) · randomized, double-blind, placebo-controlled trial, 6 weeks · n = 60
   Patients were randomly allocated to intake either 1000 mg omega-3 fatty acids from flaxseed oil plus 400 IU vitamin E supplements (n=30) or placebo (n=30) for 6 weeks. … Joint omega-3 fatty acids and vitamin E supplementation resulted in lower incidences of hyperbilirubinemia in newborns (10.3% vs. 33.3%; p=0.03).
   
   Who: women with gestational diabetes not taking oral hypoglycemic agents, and their newborns
   Effect: newborn hyperbilirubinemia 10.3% vs 33.3% (p = 0.03); higher total antioxidant capacity and nitric oxide, lower malondialdehyde
   Certainty: Same trial population as 27055970; small, short, co-supplemented with vitamin E; not powered for safety outcomes.
   Can J Diabetes, 2017 · checked 2026-10-07 · we read the abstract
5. ev-flpr-05 · Observational data · prospective cohort (biomarker sub-study) · n = 321
   Our data suggested that higher plasma levels of DHA and ALA in the first trimester were associated with increased fetal size and weight throughout subsequent pregnancy.
   
   Who: pregnant women in the NICHD Fetal Growth Studies-Singletons cohort with plasma phospholipid fatty acids measured at 10 to 14 weeks
   Effect: DHA and ALA positively associated with all fetal growth measurements; no intake data on flaxseed
   Certainty: Observational biomarker association; plasma ALA reflects many foods, not flaxseed specifically.
   EBioMedicine, 2022 · checked 2026-10-07 · we read the abstract
6. ev-flpr-06 · Position of an expert body · agency consumer fact sheet · n = —
   Some studies of the use of flaxseed during pregnancy suggest it is possibly unsafe, but the evidence is not conclusive.
   
   Who: pregnant women
   Effect: possibly unsafe in pregnancy
   Certainty: Underlying studies not named on the page; likely the Quebec preterm-birth signal for flaxseed oil (Moussally and Berard 2010), which we could not read.
   NIH National Center for Complementary and Integrative Health, Flaxseed and Flaxseed Oil (updated February 2025) · checked 2026-10-07 · we read the section
7. ev-flpr-07 · Position of an expert body · agency consumer fact sheet · n = —
   Little is known about whether it is safe to use flaxseed while breastfeeding.
   
   Who: breastfeeding women
   Effect: safety in breastfeeding unknown
   Certainty: Statement of absent evidence; LactMed monograph could not be retrieved.
   NIH National Center for Complementary and Integrative Health, Flaxseed and Flaxseed Oil (updated February 2025) · checked 2026-10-07 · we read the section
8. ev-flpr-08 · Position of an expert body · agency consumer fact sheet · n = —
   There are theoretical reasons to suspect that flaxseed or flaxseed oil might interact with other drugs, such as anticoagulant or antiplatelet drugs.
   
   Who: people taking anticoagulant or antiplatelet drugs
   Effect: theoretical interaction
   Certainty: Theoretical; no clinical cases cited. Low-dose aspirin is common in pregnancy for preeclampsia prevention.
   NIH National Center for Complementary and Integrative Health, Flaxseed and Flaxseed Oil (updated February 2025) · checked 2026-10-07 · we read the section