Norethindrone

What it is

Norethindrone is a synthetic progestin, a laboratory-made steroid that acts at the progesterone receptor. In the 0.35 mg tablet it is given continuously as a progestin-only oral contraceptive with no estrogen. Norethindrone acetate is the acetate ester of the same molecule; it is completely deacetylated to norethindrone after swallowing and, weight for weight, is twice as potent. Oral bioavailability is about 65% and the terminal half-life is roughly 8 hours.

What the research says

For contraception the evidence is reasonably solid: a 2023 review of 54 studies found a median typical-use Pearl Index of 1.63 pregnancies per 100 woman-years for progestin-only pills, much better than the 7 per 100 often quoted, though the same class of pill also produced irregular bleeding in essentially everyone in one older randomised comparison. A 2010 Cochrane review of randomised trials concluded the evidence is too thin to rank progestin-only pills against each other or against combined pills, and in one four-arm trial a levonorgestrel pill out-performed a norethisterone 350 mcg pill. For endometriosis pain the only recent randomised evidence compares norethindrone acetate against another progestin rather than against placebo. On the harm side, a 2023 UK case-control study plus meta-analysis found current or recent oral progestogen-only contraception carried a breast cancer odds ratio of 1.26, an absolute 15-year excess of roughly 8 extra cases per 100,000 users for use at 16 to 20 and about 265 per 100,000 for use at 35 to 39. Progestin-only pills were not linked to venous thromboembolism in a 2012 meta-analysis.

Evidence grade: Well established.

How it works

Drug class: 19-nortestosterone-derived progestin (progestogen). Used at 0.35 mg as a progestin-only oral contraceptive, and as norethindrone acetate at 5 mg and above as an oral progestin for gynaecological indications.

Norethindrone is a progestin. As a contraceptive it works in several ways at once: it stops ovulation in only about half of users, and the rest of the effect comes from thickening cervical mucus so sperm cannot get through, blunting the mid-cycle LH and FSH surge, slowing the egg's passage down the fallopian tube and changing the lining of the womb. At the higher norethindrone acetate doses it drives the estrogen-primed womb lining into a secretory state, which is how it is used to control bleeding and endometriosis pain. (Source 1)

What it is used for

• A 2023 review of 54 studies put the median typical-use failure rate at 1.63 pregnancies per 100 woman-years and the perfect-use rate at 0.97. The label's own figures are 0.5% perfect use and about 5% typical use. Randomised comparisons against other pills are too few to rank them. Evidence: established. (Source 2)
• Approved since long before modern trial standards. The most recent randomised evidence is a 70-patient single-centre trial against dienogest, not against placebo: both progestins reduced pain scores with no significant difference between them, and norethindrone acetate shrank endometriomas more. Evidence: limited. (Source 3)
• An approved use resting on the drug's known effect on the womb lining rather than on outcome trials; withdrawal bleeding usually follows within three to seven days of stopping. We found no modern placebo-controlled trial for this indication. Evidence: limited. (Source 4)
• Widely done in practice, but we found no systematic review or outcome trial specific to norethindrone for menstrual suppression during this search. The label is explicit that norethindrone acetate is not approved for use with estrogen in postmenopausal women for endometrial protection. Evidence: unknown. (Source 4)

Interactions

• St John's wort (Hypericum perforatum) (pharmacokinetic study): St John's wort induces CYP3A and speeds up the breakdown of norethindrone. In a 12-woman crossover study the oral clearance of norethindrone rose and breakthrough bleeding went from 2 of 12 women to 7 of 12. The authors advised expecting breakthrough bleeding and considering a barrier method. (Source 5)
• St John's wort (as stated on the label) (label): The label warns that St John's wort products may induce liver enzymes and the p-glycoprotein transporter and may make contraceptive steroids less effective, with breakthrough bleeding as a sign. (Source 6)
• Enzyme-inducing medicines: rifampin, several anticonvulsants, griseofulvin (label): Drugs that speed up the metabolism of contraceptive steroids can reduce contraceptive effect, which may show up as unintended pregnancy or breakthrough bleeding. (Source 7)
• Food (taking the tablet with or without food) (label): Unknown. The manufacturer states that the effect of food on how fast and how completely norethindrone is absorbed from this product has not been studied. (Source 8)

Stopping it

• There is no withdrawal syndrome described for the progestin-only pill. The label says the limited data show ovulation and fertility come back quickly after stopping, which is also why missed or late pills matter so much. (Source 9)
• When norethindrone acetate is used to control bleeding, a withdrawal bleed normally follows within three to seven days of stopping the tablets. (Source 4)

What goes wrong

Current or recent use of an oral progestogen-only contraceptive was associated with a slightly higher breast cancer risk, with a small absolute excess that grows with the user's age. (Source 10)

• Case-control study, Moderate certainty.
• Size: 9,498 women with incident invasive breast cancer and 18,171 matched controls, plus meta-analysis with 12 published observational studies.
• Who: Women under 50 in a UK primary care database (CPRD), 1996 to 2017.
• How long: On average 7.3 years (SD 4.6) of records before diagnosis; prescriptions on average 3.1 years before the index date.
• Result: Oral progestagen-only OR 1.26 (95% CI 1.16 to 1.37, p < 0.001); pooled RR for current or recent oral progestagen-only use 1.29 (95% CI 1.21 to 1.37); 15-year absolute excess with 5 years of use 8 per 100,000 users at ages 16-20 (0.084% to 0.093%) and about 265 per 100,000 at ages 35-39 (2.0% to 2.2%)
• Funding: not stated in the passage recorded.

Breast cancer ORs were similarly and significantly raised if the last hormonal contraceptive prescription was for oral combined, oral progestagen-only, injected progestagen, or progestagen-releasing intrauterine devices (IUDs): ORs = 1.23 (95% CI [1.14 to 1.32]; p < 0.001), 1.26 (95% CI [1.16 to 1.37]; p < 0.001), 1.25 (95% CI [1.07 to 1.45]; p = 0.004), and 1.32 (95% CI [1.17 to 1.49]; p < 0.001), respectively.

The same study put the absolute excess breast cancer risk in context: 8 extra cases per 100,000 users for five years of use in the late teens, about 265 per 100,000 for use in the late thirties. (Source 11)

• Case-control study, Moderate certainty.
• Size: Combined CPRD and previously published results.
• Who: Premenopausal women in high-income countries, UK age-specific incidence rates applied.
• How long: 15-year absolute excess after 5 years of use.
• Result: From 0.084% to 0.093% for use at ages 16 to 20; from 2.0% to 2.2% for use at ages 35 to 39.
• Funding: not stated in the passage recorded.

they suggest that the 15-year absolute excess risk of breast cancer associated with use of oral contraceptives ranges from 8 per 100,000 users (an increase in incidence from 0.084% to 0.093%) for use from age 16 to 20 to about 265 per 100,000 users (from 2.0% to 2.2%) for use from age 35 to 39.

Menstrual disturbance is the commonest adverse effect of the progestin-only pill, and ectopic pregnancies occur at about 5 per 1000 woman-years of use. (Source 12)

• Official position, Certainty not rated.
• Size: Not stated in the label passage.
• Who: Users of progestin-only oral contraceptives.
• How long: Not stated.
• Result: Frequent and irregular bleeding described as common; ectopic pregnancy incidence 5 per 1000 woman-years, with up to 10% of pregnancies reported in clinical studies being extrauterine.
• Funding: not stated (regulator-approved labelling)

Menstrual irregularity is the most frequently reported side effect. Frequent and irregular bleeding are common, while long duration of bleeding episodes and amenorrhea are less likely.

Thrombotic and thromboembolic events are listed as adverse reactions to norethindrone acetate, and active or recent clot disease is a contraindication. (Source 13)

• Official position, Certainty not rated.
• Size: Postmarketing reports; no rates given in the label.
• Who: Users of norethindrone acetate 5 mg tablets.
• How long: Not stated.
• Result: No frequencies given; events listed include deep vein thrombosis, pulmonary embolism, retinal vascular thrombosis, cerebral thrombosis and embolism, and optic neuritis which may lead to partial or complete loss of vision.
• Funding: not stated (regulator-approved labelling)

Thrombotic and thromboembolic events (e.g., deep vein thrombosis, pulmonary embolism, retinal vascular thrombosis, cerebral thrombosis and embolism)

What the evidence supports

Across 54 studies, progestin-only pills including norethindrone failed less often in typical use than the commonly quoted 7 per 100 woman-years. (Source 2)

• Systematic review, Low certainty.
• Size: 54 studies included; analyses restricted to those at low or moderate risk of bias.
• Who: Women using progestin-only pills; norethindrone 0.35 mg formulations were among those included.
• How long: Pearl Index and life-table rates over the study periods reported, typically 1 year.
• Result: Median typical-use Pearl Index 1.63 (range 0.00-14.20, IQR 4.03); median perfect-use (method failure) Pearl Index 0.97 (range 0.40-6.50, IQR 0.68); excluding desogestrel and drospirenone the median typical-use rate was 2.00.
• Funding: not stated.

Among studies at low or moderate risk of bias, the median Pearl Index rate (the failure rate during typical use) was 1.63 (range 0.00-14.20, IQR 4.03) and the median method failure Pearl Index rate (the failure rate during perfect use) was 0.97 (range 0.40-6.50, IQR 0.68).

In the only recent randomised trial, norethindrone acetate 5 mg daily reduced endometriosis pain as much as dienogest, with fewer dropouts, but there was no placebo group. (Source 14)

• Randomized trial, Low certainty.
• Size: 70 patients (30 norethindrone acetate, 40 dienogest); 16 and 18 respectively completed treatment.
• Who: Women aged 18-40 attending a single endometriosis clinic, April 2022 to April 2023.
• How long: 12 months, with assessments at 6 and 12 months.
• Result: Baseline dysmenorrhoea 7.43 +/- 2.9 (norethindrone acetate) and 7.23 +/- 2.87 (dienogest) on a visual analogue scale, both 0.00 +/- 0.00 at 12 months; chronic pelvic pain 1.06 +/- 2.43 vs 0.00 +/- 0.00 (p = 0.058); greater endometrioma shrinkage with norethindrone acetate (p = 0.037); 6-month dropout 23.3% vs 47.5% (p = 0.026)
• Funding: not stated.

Both groups showed significant reductions in pain scores at all follow-ups, with no significant differences between them.

What the evidence does not support

Cochrane found the randomised evidence too sparse to say whether progestin-only pills work as well as combined pills or as each other, and in one trial a norethisterone pill was less effective than a levonorgestrel pill. (Source 15)

• Systematic review, Very low certainty.
• Size: 6 randomised trials met inclusion criteria; studies could not be pooled.
• Who: Women using progestin-only pills for contraception.
• How long: Varied by trial; not pooled.
• Result: No meta-analysis possible because of disparate exposures; in a four-arm trial the levonorgestrel 30 mcg pill had higher efficacy than the norethisterone 350 mcg pill; in the ethynodiol diacetate comparison irregular cycles occurred in all women on the progestin-only pill (odds ratio 135.96, 95% CI 7.61 to 2421.02)
• Funding: not stated.

Evidence is insufficient to compare progestin-only pills to each other or to combined oral contraceptives.

In the one trial that compared them head to head, a levonorgestrel 30 mcg progestin-only pill was more effective than a norethisterone 350 mcg pill. (Source 16)

• Systematic review, Very low certainty.
• Size: One four-arm randomised trial inside a Cochrane review of 6 trials.
• Who: Women using oral contraception.
• How long: Not stated in the review's abstract.
• Result: The progestin-only pill containing levonorgestrel 30 mcg had higher efficacy than the pill containing norethisterone 350 mcg; the review could not pool any of its six trials because the exposures were too different.
• Funding: not stated.

Limit of this finding: The abstract prints the mcg symbol as "mug", so the doses are 30 mcg of levonorgestrel and 350 mcg of norethisterone. This is one trial inside a review that could not combine its studies statistically, so it is weak evidence about one pill versus another rather than a settled ranking.

In a trial comparing two progestin-only and two combined oral contraceptives, the progestin-only pill containing levonorgestrel 30 mug had higher efficacy than did the pill containing norethisterone 350 mug.

Progestin-only pills were not associated with venous thromboembolism, although injectable progestins were. (Source 17)

• Meta-analysis, Low certainty.
• Size: 8 observational studies; 147 women had a venous thromboembolic event while taking progestin-only contraception.
• Who: Women using progestin-only contraception compared with non-users of hormonal contraception.
• How long: Varied by study.
• Result: Overall adjusted relative risk 1.03 (95% CI 0.76 to 1.39); progestin-only pills 0.90 (0.57 to 1.45); progestin intrauterine device 0.61 (0.24 to 1.53); injectable progestin 2.67 (1.29 to 5.53)
• Funding: not stated.

Limit of this finding: The injectable-progestin figure, 2.67 (1.29 to 5.53), rests on a subgroup of eight observational studies in which only 147 women in total had a clot, so the plausible range is very wide. The authors themselves say that association "requires further study". No randomised trials were included, so none of these numbers show cause and effect, and the pill result (0.90, 0.57 to 1.45) is the part that applies to norethindrone taken by mouth.

Subgroup analysis confirmed there was no association between venous thromboembolic risk and progestin-only pills (relative risk 0.90 (0.57 to 1.45))

Whether hormonal contraceptives change later fracture risk cannot be answered from the existing randomised evidence, which measured bone density rather than fractures. (Source 18)

• Systematic review, Moderate certainty.
• Size: 19 randomised controlled trials; no trial had fracture as an outcome.
• Who: Premenopausal women using hormonal contraceptives.
• How long: Varied; bone density measured in 17 studies.
• Result: No fracture outcomes; depot medroxyprogesterone acetate was associated with decreased bone mineral density, combined oral contraceptives did not appear to affect it negatively; GRADE quality moderate overall and low for the combined-pill evidence.
• Funding: not stated.

Limit of this finding: The review's conclusion is about fractures, but none of its 19 trials actually measured fractures - they measured bone density and bone-turnover markers. So "cannot be determined from existing information" means no trial looked at fractures, not that trials looked and found nothing. Read it as an absence of evidence, not evidence of absence.

Whether steroidal contraceptives influence fracture risk cannot be determined from existing information.

None of the 19 randomised trials in that review measured fractures at all; they measured bone density and bone-turnover markers instead. (Source 19)

• Systematic review, Moderate certainty.
• Size: 19 randomised controlled trials.
• Who: Women using hormonal contraception before menopause.
• How long: Varied between trials; not stated in the abstract.
• Result: No trial had fracture as an outcome; bone mineral density was measured in 17 studies and 12 trials assessed biochemical markers of bone turnover; depot medroxyprogesterone acetate was associated with decreased bone mineral density, while combined oral contraceptives did not appear to affect it negatively.
• Funding: not stated.

No trial had fracture as an outcome. BMD was measured in 17 studies and 12 trials assessed biochemical markers of bone turnover.

Where the research disagrees

How well progestin-only pills actually work in everyday use

• Zuniga and colleagues, Contraception 2023, systematic review of 54 studies: Among studies at low or moderate risk of bias, the median Pearl Index rate during typical POP use was much lower than currently estimated (7.00), while the median perfect use rate was similar to current estimates. (Source 2)
• FDA-approved labelling for norethindrone 0.35 mg (Teva, 2022), regulatory position citing conventional typical-use estimates: If used perfectly, the first-year failure rate for progestin-only oral contraceptives is 0.5%. However, the typical failure rate is estimated to be closer to 5%, due to late or omitted pills. (Source 20)

Whether progestin-only contraception raises breast cancer risk

• Fitzpatrick and colleagues, PLOS Medicine 2023, nested case-control study plus meta-analysis of observational studies: This study provides important new evidence that current or recent use of progestagen-only contraceptives is associated with a slight increase in breast cancer risk, which does not appear to vary by mode of delivery, and is similar in magnitude to that associated with combined hormonal contraceptives. (Source 21)
• The same authors, on how to weigh it, observational data, so association rather than proven cause: Such risks need be balanced against the benefits of using contraceptives during the childbearing years. (Source 22)

How much

• Reference intake: Dose is set by the prescriber, not by the reader. As a position, the FDA-approved labelling for the 0.35 mg progestin-only contraceptive (Teva, revised February 2022) describes a continuous regimen of 0.35 mg norethindrone daily taken at the same time each day. (Source 23)
• Upper limit: There is no upper intake level in the nutritional sense. As a position, the norethindrone acetate label (Teva) describes escalation for endometriosis to a maximum of 15 mg per day. (Source 4)
• Studied: The 2025 randomised trial in endometriosis gave norethindrone acetate 5 mg daily for 12 months. (Source 3)
• Studied: The contraceptive trials pooled in the 2023 review used progestin-only pills taken continuously; norethindrone 0.35 mg formulations were among them. (Source 2)
• Studied: The 2003 interaction study gave a combined pill containing 1 mg norethindrone with ethinyl estradiol for three cycles, with St John's wort 300 mg three times a day during two of them. (Source 24)

A common belief, and what the research shows

The belief: The mini-pill is much less reliable than the combined pill, and it works by stopping ovulation.

What the research shows: Neither half holds up well. On reliability, Cochrane's randomised evidence could not separate them at all: "Evidence is insufficient to compare progestin-only pills to each other or to combined oral contraceptives." And the review of 54 studies found typical-use failure well below the 7 per 100 figure often quoted. On mechanism, the label itself says ovulation is only suppressed in about half of users: "Nora-BE progestin-only oral contraceptives prevent conception by suppressing ovulation in approximately half of users, thickening the cervical mucus to inhibit sperm penetration, lowering the mid-cycle LH and FSH peaks, slowing the movement of the ovum through the fallopian tubes, and altering the endometrium."

Questions and answers

What is it?

Norethindrone is a man-made progestin, a steroid hormone modelled on progesterone. At 0.35 mg it is taken every day as a progestin-only contraceptive pill with no estrogen in it. Norethindrone acetate is the same molecule with an acetate group attached; the body strips that off straight away, and weight for weight it is twice as strong as plain norethindrone. (Source 23)

What does it do in the body?

It acts at progesterone receptors. As a contraceptive it works through several effects at once rather than one: it blocks ovulation in only about half of users, and otherwise thickens cervical mucus, blunts the mid-cycle hormone surge, slows the egg's passage along the tube and changes the womb lining. At the higher acetate doses that last effect is the point, which is how it is used for heavy or irregular bleeding and for endometriosis. (Source 1)

Is it good or bad for you?

It depends on what it is for and on who is taking it. For contraception the failure rate in real use looks better than the figure usually quoted, and it does not appear to raise clot risk the way injectable progestins do. Against that, irregular bleeding is very common, and a 2023 UK study plus meta-analysis found a slightly raised breast cancer risk during and shortly after use, small in absolute terms for younger users and larger for women in their late thirties. The researchers themselves framed it as a trade-off. (Source 22)

How do you get more of it?

It is a prescription medicine, so the amount is set by a prescriber and not by the reader. The progestin-only contraceptive is taken continuously, one tablet at the same time every day with no break, and the label is blunt that timing is what makes it work. There is no food or supplement route to it. (Source 25)

If it is harmful, what reduces it?

The drug leaves the body on its own once it is stopped: the terminal half-life is about 8 hours, so most of a dose has gone within a day or so, which is why the contraceptive effect depends on taking it daily. Fertility returns quickly after stopping. There is no antidote or binding agent described in the literature we read. (Source 26)

Why might someone be low in it or missing it?

This is a drug, not a nutrient, so nobody is deficient in it. Someone may not be given it because of the conditions listed as contraindications, including known or suspected pregnancy, breast cancer, undiagnosed abnormal genital bleeding, liver tumours or acute liver disease. Its effect can also be undercut by enzyme-inducing drugs such as rifampin, some anticonvulsants, and St John's wort. (Source 27)

Which whole foods contain it or feed it?

None. Norethindrone is a synthetic steroid manufactured as a tablet; it is not a constituent of food and no food raises or lowers your level of it. The nearest thing the label says about food is that the effect of eating on absorption of this particular product was never studied. (Source 8)

We searched: We searched for norethindrone or norethisterone food sources and food-effect studies via Europe PMC and read the FDA labelling for norethindrone 0.35 mg and norethindrone acetate 5 mg; neither describes a dietary source, because the compound is synthetic.

What happens if you do not have it?

Nothing happens from not having the drug itself, since it is not something the body needs. What changes is the condition it was treating. Without contraception there is a risk of pregnancy; the label puts the first-year failure rate for progestin-only pills at about 0.5% with perfect use and nearer 5% in typical use, mostly from late or missed pills. If it was being taken for endometriosis pain or abnormal bleeding, those symptoms can come back, and a withdrawal bleed usually follows within three to seven days of stopping the acetate tablets. (Source 20)

How can you test for it?

There is no routine blood test used to check whether norethindrone is at the right level or working. Response is judged clinically, by bleeding pattern, symptoms and absence of pregnancy. Progestin-only pills do shift some endocrine laboratory results, for instance lowering sex hormone-binding globulin, which matters if such tests are being interpreted for another reason. (Source 28)

References

1. DailyMed / Teva Pharmaceuticals, Inc. (FDA label). NORA-BE (norethindrone tablets USP 0.35 mg) - prescribing information. 2022. Read the source
2. Contraception. Effectiveness and efficacy rates of progestin-only pills: A comprehensive literature review. 2023. PMID 36535414, DOI 10.1016/j.contraception.2022.109925. Read the source
3. European journal of obstetrics, gynecology, and reproductive biology. Norethindrone acetate versus dienogest for pain relief in endometriosis related pain: A randomized controlled trial. 2025. PMID 40233572, DOI 10.1016/j.ejogrb.2025.113940. Read the source
4. DailyMed / Teva Pharmaceuticals USA, Inc. (FDA label). NORETHINDRONE ACETATE tablets, USP 5 mg - prescribing information. 2022. Read the source
5. Clinical pharmacology and therapeutics. The interaction between St John's wort and an oral contraceptive. 2003. PMID 14663455, DOI 10.1016/j.clpt.2003.08.009. Read the source
6. DailyMed / Teva Pharmaceuticals, Inc. (FDA label). NORA-BE (norethindrone tablets USP 0.35 mg) - prescribing information, pharmacokinetics, interactions and discontinuation sections. 2022. Read the source
7. DailyMed / Teva Pharmaceuticals, Inc. (FDA label). NORA-BE (norethindrone tablets USP 0.35 mg) - prescribing information, pharmacokinetics, interactions and discontinuation sections. 2022. Read the source
8. DailyMed / Teva Pharmaceuticals, Inc. (FDA label). NORA-BE (norethindrone tablets USP 0.35 mg) - prescribing information, pharmacokinetics, interactions and discontinuation sections. 2022. Read the source
9. DailyMed / Teva Pharmaceuticals, Inc. (FDA label). NORA-BE (norethindrone tablets USP 0.35 mg) - prescribing information, contraindications, laboratory tests and fertility sections. 2022. Read the source
10. PLOS Medicine. Combined and progestagen-only hormonal contraceptives and breast cancer risk: A UK nested case-control study and meta-analysis. 2023. PMID 36943819, DOI 10.1371/journal.pmed.1004188. Read the source
11. PLOS Medicine. Combined and progestagen-only hormonal contraceptives and breast cancer risk: A UK nested case-control study and meta-analysis. 2023. PMID 36943819, DOI 10.1371/journal.pmed.1004188. Read the source
12. DailyMed / Teva Pharmaceuticals, Inc. (FDA label). NORA-BE (norethindrone tablets USP 0.35 mg) - prescribing information. 2022. Read the source
13. DailyMed / Teva Pharmaceuticals USA, Inc. (FDA label). NORETHINDRONE ACETATE tablets, USP 5 mg - prescribing information. 2022. Read the source
14. European journal of obstetrics, gynecology, and reproductive biology. Norethindrone acetate versus dienogest for pain relief in endometriosis related pain: A randomized controlled trial. 2025. PMID 40233572, DOI 10.1016/j.ejogrb.2025.113940. Read the source
15. The Cochrane database of systematic reviews. Progestin-only pills for contraception. 2010. PMID 20091638, DOI 10.1002/14651858.CD007541.pub2. Read the source
16. The Cochrane database of systematic reviews. Progestin-only pills for contraception. 2010. PMID 20091638, DOI 10.1002/14651858.CD007541.pub2. Read the source
17. BMJ (Clinical research ed.). Assessing the risk of venous thromboembolic events in women taking progestin-only contraception: a meta-analysis. 2012. PMID 22872710, DOI 10.1136/bmj.e4944. Read the source
18. The Cochrane database of systematic reviews. Steroidal contraceptives: effect on bone fractures in women. 2014. PMID 24960023, DOI 10.1002/14651858.CD006033.pub5. Read the source
19. The Cochrane database of systematic reviews. Steroidal contraceptives: effect on bone fractures in women. 2014. PMID 24960023, DOI 10.1002/14651858.CD006033.pub5. Read the source
20. DailyMed / Teva Pharmaceuticals, Inc. (FDA label). NORA-BE (norethindrone tablets USP 0.35 mg) - prescribing information. 2022. Read the source
21. PLOS Medicine. Combined and progestagen-only hormonal contraceptives and breast cancer risk: A UK nested case-control study and meta-analysis. 2023. PMID 36943819, DOI 10.1371/journal.pmed.1004188. Read the source
22. PLOS Medicine. Combined and progestagen-only hormonal contraceptives and breast cancer risk: A UK nested case-control study and meta-analysis. 2023. PMID 36943819, DOI 10.1371/journal.pmed.1004188. Read the source
23. DailyMed / Teva Pharmaceuticals, Inc. (FDA label). NORA-BE (norethindrone tablets USP 0.35 mg) - prescribing information, pharmacokinetics, interactions and discontinuation sections. 2022. Read the source
24. Clinical pharmacology and therapeutics. The interaction between St John's wort and an oral contraceptive. 2003. PMID 14663455, DOI 10.1016/j.clpt.2003.08.009. Read the source
25. DailyMed / Teva Pharmaceuticals, Inc. (FDA label). NORA-BE (norethindrone tablets USP 0.35 mg) - prescribing information, contraindications, laboratory tests and fertility sections. 2022. Read the source
26. DailyMed / Teva Pharmaceuticals, Inc. (FDA label). NORA-BE (norethindrone tablets USP 0.35 mg) - prescribing information, pharmacokinetics, interactions and discontinuation sections. 2022. Read the source
27. DailyMed / Teva Pharmaceuticals, Inc. (FDA label). NORA-BE (norethindrone tablets USP 0.35 mg) - prescribing information, contraindications, laboratory tests and fertility sections. 2022. Read the source
28. DailyMed / Teva Pharmaceuticals, Inc. (FDA label). NORA-BE (norethindrone tablets USP 0.35 mg) - prescribing information, contraindications, laboratory tests and fertility sections. 2022. Read the source