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Natural Cycles is an FDA-cleared contraception app at $79.99 a year, using basal body temperature and cycle data to identify fertile days. We are reviewing it because of something most GLP-1 patients have never been told: these medications interfere with oral contraceptives, and they are contraindicated in pregnancy. That makes contraception a live question — and this app is both better and worse suited to it than you might expect.
The Warning Most GLP-1 Patients Have Not Been Given
Tirzepatide’s FDA label instructs patients using oral hormonal contraceptives to switch to a non-oral method, or add a barrier method, for four weeks after starting and for four weeks after each dose escalation.
The cause is delayed gastric emptying reducing absorption. The effect is largest after the first dose and diminishes over time. Reported reductions in ethinyl estradiol exposure are around 20% with tirzepatide at 5mg and about 12% with semaglutide, and both labels carry backup-contraception guidance.
This is not a fringe concern. Regulators including the UK’s MHRA and Australia’s TGA have issued specific contraception advice for people taking these medicines, and reproductive health bodies have published guidance on the interaction.
Set that alongside the other half: GLP-1 medications are not for use in pregnancy, and guidance is to discontinue one to two months before attempting conception. So you have a medication that both reduces the reliability of the most commonly used contraceptive and must not be taken if you conceive.
Across the seventy-plus GLP-1 providers we have reviewed, we have seen this addressed almost nowhere. If you are of reproductive age and taking one of these medications, raise it with your prescriber — particularly in the four weeks after every dose increase. Our side effects guide covers the wider picture.
Where Natural Cycles Has a Real Advantage
Natural Cycles involves nothing you swallow. Delayed gastric emptying cannot reduce the absorption of a method that has no absorption — so the specific interaction that undermines oral contraceptives on a GLP-1 simply does not apply.
That is a genuine, non-obvious point in its favour, and the same logic applies to IUDs, implants and barrier methods. If the pill is your current method and you have just started tirzepatide, switching to something non-oral is exactly what the label asks for.
It is also hormone-free, which some people prefer while their body is already undergoing substantial change, and it is FDA-cleared rather than an unregulated tracking app.
And Where Rapid Weight Loss Breaks It
The algorithm depends on cycle regularity and basal body temperature. Rapid weight loss commonly disrupts menstrual cycles — which degrades precisely the signal Natural Cycles needs to work.
This is the counterpoint, and it is not a minor one. Substantial or fast weight loss can make cycles irregular, longer, shorter or absent. Fertility-awareness methods perform worst exactly when cycles are unpredictable, because the algorithm has less to work with and errs by widening the fertile window — or, worse, by misidentifying it.
There is a further wrinkle worth knowing: weight loss can restore ovulation in people whose cycles had stopped, particularly with PCOS. Someone who was not ovulating, and who reasonably assumed they were unlikely to conceive, may become fertile again with no warning — part of why unexpected pregnancies on these medications have been so widely discussed.
So the honest position is: Natural Cycles avoids the absorption problem and runs into a cycle stability problem. Both are consequences of the same medication.
What 93% Actually Means Here
Natural Cycles reports 93% effectiveness with typical use and 98% with perfect use — meaning never having unprotected sex on a flagged fertile day. Typical use is the honest number, because it reflects how people actually behave.
Ninety-three percent means roughly seven pregnancies per hundred users per year. In ordinary circumstances that is comparable to the pill in typical use and a reasonable trade for being hormone-free. On a GLP-1 the circumstances are not ordinary: the medication is contraindicated in pregnancy, so the consequence of method failure is not just an unplanned pregnancy but an unplanned pregnancy while taking a drug you would need to stop immediately.
If pregnancy would be a serious problem for you right now, that argues for a method in the greater-than-99% band — an IUD or implant, both of which are also non-oral and therefore unaffected by gastric emptying. This is a conversation for a clinician rather than an article.
Price
| Plan | Cost | Thermometer |
|---|---|---|
| Annual | $79.99/year | Included free |
| Monthly | $9.99/month | Not included |
The annual plan is clearly the better buy given the thermometer is included and the monthly rate works out higher. It is modest money compared with most of what we review — though contraception is often free or very cheap through insurance, which is the more relevant comparison.
Pros and Cons
Pros
- Not affected by the delayed gastric emptying that undermines oral contraceptives
- FDA-cleared, unlike most cycle-tracking apps
- Hormone-free
- Clinical evidence behind the effectiveness figures
- $79.99 a year including a thermometer
- Builds genuine awareness of your own cycle
Cons
- Rapid weight loss disrupts the cycle regularity the algorithm needs
- 93% typical use is well below IUD or implant reliability
- GLP-1s are contraindicated in pregnancy, raising the cost of failure
- Requires consistent daily temperature measurement
- Illness and disrupted sleep also affect readings — both common during titration
- Provides no protection against sexually transmitted infections
Who Should Use It, and Who Should Not
Natural Cycles suits you if your cycles are regular and stable, your weight is no longer changing rapidly, you want a hormone-free non-oral method, and an unplanned pregnancy would be manageable rather than serious. On those terms it is a well-built, FDA-cleared product.
Do not rely on it if you are in an active phase of rapid weight loss — the cycle irregularity that causes is the algorithm’s weakest point — or if pregnancy would be a serious problem while you are on a medication contraindicated in pregnancy. In that situation a long-acting method is the better answer, and it is also non-oral.
And regardless of what you choose: if you take the pill and have just started or increased tirzepatide, use a barrier method for four weeks. That is the label instruction, not our advice.
Limitations of This Review
This review is based on published pricing, the products’ own effectiveness data and secondary reporting of FDA labelling and regulatory guidance, checked on 7 August 2026. We did not read the Mounjaro label or the underlying pharmacokinetic studies directly; verify the contraception guidance with your prescriber or the current prescribing information. The effectiveness percentages are as published by Natural Cycles. No study we are aware of has examined fertility-awareness method performance specifically in people undergoing rapid GLP-1 weight loss — our concern about cycle disruption is a reasoned inference. Nothing here is contraceptive advice for your situation.
Frequently Asked Questions
Does my GLP-1 affect my birth control pill?
It can. Tirzepatide’s label instructs oral contraceptive users to switch to a non-oral method or add a barrier for four weeks after starting and after each dose increase, because delayed gastric emptying reduces absorption. Semaglutide shows a smaller but similar effect. Speak to your prescriber.
Can I take a GLP-1 if I might get pregnant?
These medications are not for use in pregnancy, and guidance is to discontinue one to two months before attempting conception. If you are of reproductive age, effective contraception is part of taking them safely.
Will Natural Cycles still work while I am losing weight?
Less reliably. The algorithm depends on cycle regularity and basal body temperature, and rapid weight loss commonly makes cycles irregular. Illness and poor sleep during titration also affect temperature readings.
Could weight loss make me more fertile?
Yes. Weight loss can restore ovulation in people whose cycles had stopped, particularly with PCOS. Someone who assumed they were unlikely to conceive may become fertile again without realising — which is worth planning for rather than discovering.
Verdict
3.3 / 5
A well-built, FDA-cleared method that sidesteps the GLP-1 absorption problem and runs straight into the cycle-disruption one — at a moment when pregnancy is contraindicated.
The most valuable thing on this page is not the rating. It is that GLP-1 medications reduce oral contraceptive absorption, that tirzepatide’s label requires backup contraception for four weeks after every dose escalation, that the drugs are contraindicated in pregnancy, and that weight loss can restore fertility in people who had stopped ovulating. Almost none of the providers we have reviewed mentions any of it.
Natural Cycles genuinely helps with one half of that and is weakened by the other. If your weight has stabilised and your cycles are regular, it is a reasonable hormone-free choice. If you are mid-titration and pregnancy would be a serious problem, choose something that does not depend on a cycle your medication is disrupting.
Medical Disclaimer & Review Date
This review is general consumer information, not medical advice. GLP-1 medications are prescription drugs with serious contraindications, and whether any treatment is appropriate for you is a decision only a licensed healthcare provider who knows your medical history can make. Nothing here should be used to start, stop, or change a medication.
Details in this review come from Natural Cycles's own published materials as of the date below. Pricing, medication availability, state coverage, and policies in this category change frequently — verify current terms directly with the provider before purchasing.
Date reviewed: August 7, 2026
Raise Contraception at Your Next Dose Increase
Tirzepatide’s label asks for a barrier method for four weeks after every escalation. If nobody has told you that, it is worth asking why.