Norethindrone and ethinyl estradiol and Phentermine and topiramate interaction
Norethindrone and ethinyl estradiol and Phentermine and topiramate: both prescribing labels flag this combination with the strongest language, such as a contraindication, a boxed warning, or an instruction to avoid it.
Do not combine without a prescriber's guidance. The label language below is the strongest FDA uses.
What the FDA labels say
From the Norethindrone and ethinyl estradiol (Lo Loestrin Fe) label · effective 2025-03-07
Counsel patients to use a back-up method or alternative method of contraception when enzyme inducers are used with COCs ( 7.1 ) -- - ---------- ------ USE IN SPECIFIC POPULATIONS---- -- -- --------- ---- Lactation: Not recommended; Lo Loestrin Fe can decrease milk production ( 8.2 )
John’s wort topiramate HIV protease inhibitors and non-nucleoside reverse transcriptase inhibitors : Significant changes (increase or decrease) in the plasma levels of the estrogen and progestin have been noted in some cases of co-administration of HIV protease inhibitors or of non-nucleoside reverse transcriptase inhibitors.
From the Phentermine and topiramate label · effective 2026-05-18
Oral Contraceptives Clinical Impact Co-administration of multiple-dose phentermine and topiramate extended-release capsules 15 mg/92 mg once daily with a single dose of oral contraceptive containing 35 µg ethinyl estradiol (estrogen component) and 1 mg norethindrone (progestin component), in obese otherwise healthy volunteers, decreased the exposure of ethinyl…
Although this interaction is not anticipated to increase the risk of pregnancy, irregular bleeding (spotting) may occur more frequently due to both the increased exposure to the progestin and lower exposure to the estrogen, which tends to stabilize the endometrium.
Oral Contraceptives : Altered exposure of progestin and estrogen may cause irregular bleeding, but not increased risk of pregnancy.
Intervention Inform patients not to discontinue their combination oral contraceptive if spotting occurs, but to notify their health care provider if the spotting is troubling to them.
Advise patients not to discontinue oral contraceptives if spotting occurs ( 7 ).
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Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.