In 1 trial, breakthrough bleeding rose from 2 of 12 women to 7 of 12 when this herb was added to the pill. Bleeding was not the only change.
Another trial found follicle growth and probable ovulation, which is the change that matters.
Quick Answer: Does St. John's Wort Affect Birth Control?
Yes, it can make the combined pill less reliable. It speeds up the breakdown of the pill's hormones through CYP3A4, and trials found more breakthrough bleeding and, in 1 study, probable ovulation. A 2003 trial advised adding a barrier method. Other hormonal methods have not been tested, so ask your prescriber.
Key Takeaways
- Breakthrough bleeding rose from 2 of 12 to 7 of 12 women.
- Another trial saw bleeding climb from 35% to as high as 88%.
- 1 study of 16 women found follicle growth and probable ovulation.
- All 4 trials in a review tested combined pills only.
- Enzyme activity took about 7 days to settle after stopping.
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Why the Pill Is Affected
Both hormones in a combined pill are cleared by CYP3A4, the enzyme this herb switches on.
- The hormones: Ethinyl estradiol plus a progestin.
- The enzyme: CYP3A4, which clears both of them.
- The effect: Faster breakdown and lower hormone levels.
- The first sign: Usually breakthrough bleeding.
A 2016 systematic review described the herb as a strong CYP3A4 inducer and noted that both pill components are CYP3A4 substrates.[1]Co-administration of St. John's wort and hormonal contraceptives: a systematic review — Contraception (2016) View source
What the herb is used for in the first place is in a plain account of the herb.
What the Trials Found
The evidence is small, and it points the same way.
| Trial | Women | Finding |
|---|---|---|
| 2003, norethindrone 1/35 pill | 12 | Bleeding in 2 of 12, then 7 of 12; estrogen half-life 23.4 to 12.2 hours |
| 2003, low-dose desogestrel pill | 18 | Bleeding 35%, then 77% and 88%; progestin exposure down about 42 to 44% |
| 2005, norethindrone 1/20 pill | 16 | Exposure down 13 to 15%; follicle growth and probable ovulation |
| 2016 review | 4 studies | 3 of 4 showed more breakthrough bleeding |
In the first 2003 trial, breakthrough bleeding rose from 2 of 12 women to 7 of 12, and the authors advised considering a barrier method.[2]The interaction between St John's wort and an oral contraceptive — Clinical Pharmacology and Therapeutics (2003) View source
In the second, bleeding between periods rose from 35% on the pill alone to 77% and 88%, depending on the dose of the herb.[3]Interaction of St John's wort with low-dose oral contraceptive therapy: a randomized controlled trial — British Journal of Clinical Pharmacology (2003) View source
Bleeding Versus Ovulation
Breakthrough bleeding is a warning sign, not proof that the pill has failed.
- Bleeding: More common in 3 of the 4 trials.
- Ovulation: Probable in 1 trial, not seen in another.
- Why it matters: Stopping ovulation is what the pill is for.
- Bleeding matters too: It leads some people to stop the pill.
The 2005 trial found a 13 to 15% drop in hormone exposure, with follicle growth and probable ovulation during the herb cycles.[4]Interaction of St. John's Wort with oral contraceptives: effects on the pharmacokinetics of norethindrone and ethinyl estradiol, ovarian activity and breakthrough bleeding — Contraception (2005) View source
The same enzyme lowers many other drugs too, and those are in the wider list of affected medicines.
If You Want to Take It Anyway
Some people will decide the herb is worth it. These steps follow the trials.
- Tell: Your prescriber or pharmacist before you start.
- Back up: The 2003 trial advised a barrier method.
- After stopping: Enzyme activity took about 7 days to return.
- Watch: New breakthrough bleeding is a signal to check.
After 14 days on the herb, CYP3A activity took about 7 days to return to its starting level.[6]The recovery time-course of CYP3A after induction by St John's wort administration — British Journal of Clinical Pharmacology (2008) View source
The herb has other side effects worth knowing, though none is as consequential as this one.
Other Hormonal Methods
The trials used combined pills. Other methods are a gap in the evidence, not a green light.
- Implant, injection, patch and ring: Not tested with this herb in these trials.
- Hormonal IUD: Not tested either.
- Copper IUD and condoms: No hormone for the enzyme to clear.
- The rule: Ask whoever prescribed your method.
The US government's complementary health centre lists birth control pills among the medicines this herb can weaken.[5]St. John's Wort: Usefulness and Safety — National Center for Complementary and Integrative Health View source
For someone using only a copper IUD or condoms, the St. John's Wort we sell raises no contraceptive question, though the full medicine check still applies.
Mood, the Pill and the Real Choice
Many people try this herb for low mood, and many of the same people take the pill. That overlap is why this page exists.
- Low mood: Ask a clinician about options that leave contraception alone.
- No hormonal method: The pill interaction does not apply.
- Blends: Check them, as some contain the herb.
- Never assume: That herbal means it cannot interact.
If mood is the reason you reached for this herb, that conversation with a clinician is also the place to raise contraception.
Speak to a Clinician Before Taking St. John's Wort If
- You take any prescription medicine, because this herb speeds up how the body clears many of them
- You take an antidepressant or any other medicine that acts on serotonin
- You rely on the pill or another hormonal method to prevent pregnancy
- You take warfarin, digoxin, cyclosporine, tacrolimus or any HIV medicine
- You are pregnant or breastfeeding, or have ever had a manic episode
- You have any thought of self-harm, which needs same-day help: call or text 988 in the US
Frequently Asked Questions
What herbs should I avoid while on birth control pills? +
St. John's Wort is the best documented, with 4 trials in a 2016 review. Ask a pharmacist about any other herb you take.
How long does it take for St Johns wort to affect birth control? +
The trials added it for 1 or 2 cycles. Induction builds over days: digoxin data show no effect after 1 dose but a clear one by day 10.
What supplements should you not take with birth control pills? +
St. John's Wort heads the list, because it speeds up how CYP3A4 clears both pill hormones. Check blends for it, including 1 of our own, Depression Tamer.
What cancels out birth control pills? +
Nothing simply cancels it, but enzyme inducers can lower hormone levels. With this herb, trials found more bleeding and, in 1 study, probable ovulation.
Does St. John's wort affect estrogen levels? +
It speeds up clearance of the pill's estrogen. In 1 trial its half-life fell from 23.4 to 12.2 hours.
Does St. John's Wort affect the implant or IUD? +
The 4 trials in a 2016 review all used combined pills. For implants, injections and hormonal IUDs there are no trial data, so ask your prescriber.
Should I use a backup method? +
If you take both, yes. The 2003 trial advised adding a barrier method after bleeding rose from 2 to 7 of 12 women.
How long after stopping should I keep a backup method? +
Enzyme activity took about 7 days to return to normal in 1 study. Ask a pharmacist for the period that fits your method.
Does a low-hyperforin product avoid the problem? +
It may reduce it: the 1 study with no hormone change used a product low in hypericin. That is too little evidence to rely on.
What is breakthrough bleeding? +
Bleeding between periods while on the pill. In 1 trial with this herb it rose from 35% to as high as 88% of women.
Related Reading
- Is It as Effective as an SSRI?
- How Much St. John's Wort the Trials Used
- St. John's Wort With Sertraline or Lexapro
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