Natural Cycles Review: And Why Fertility Changes on a GLP-1
Natural Cycles is a subscription app that uses daily basal body temperature — from a thermometer or a compatible wearable — with cycle data to identify fertile and non-fertile days. It is the first app cleared by the FDA as a contraceptive, and the company states 98% effectiveness with perfect use and 93% with typical use. For readers of this site there is an urgent adjacent fact: GLP-1 medication can change fertility, and it is not safe in pregnancy.
Verified August 25, 2026. Natural Cycles is a contraceptive app. It does not protect against sexually transmitted infections. For weight-loss medication see our GLP-1 provider rankings.
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Verdict: A real regulatory clearance behind a method whose effectiveness depends heavily on the user. FDA clearance as a contraceptive is a genuine distinction in a category full of general cycle-tracking apps that carry no such status. The published figures deserve reading precisely: 93% with typical use means roughly seven pregnancies per hundred users per year — better than nothing and materially worse than an IUD or implant. It requires consistent daily measurement, tolerance of red days, and no protection against infection. For someone with a shift-work pattern, disrupted sleep or irregular cycles, it will produce many more fertile-flagged days.
What Natural Cycles Costs
Subscription plus a measuring device.
| Plan | What you get | Listed | Real cost |
|---|---|---|---|
| Monthly plan | App subscription | Monthly | Device extra |
| Annual plan | App subscription | Annual | Lower per month |
| Measuring device | Thermometer or wearable | Additional | Required |
| Effectiveness | Company's published figures | 98% perfect / 93% typical | Read both numbers |
GLP-1 medication changes fertility and is not for use in pregnancy
Three specific things. Weight loss and improved insulin sensitivity can restore ovulation in people with polycystic ovary syndrome who were not ovulating regularly before, which has produced a wave of unplanned pregnancies among people who believed they could not conceive easily. Tirzepatide delays gastric emptying, which can reduce absorption of oral contraceptives — labelling advises a non-oral method or an added barrier method for four weeks after starting and after each dose increase. And these medicines are not for use in pregnancy: because semaglutide has a long half-life, labelling advises discontinuing at least two months before a planned pregnancy. If you are on a GLP-1 and could become pregnant, contraception is a conversation to have with your prescriber now rather than later.
Compare against long-acting reversible methods on effectiveness rather than on convenience if avoiding pregnancy is the priority.
Reading the effectiveness figures honestly
Perfect use describes the method followed exactly, every measurement taken, every red day observed. Typical use describes what happens in real life, and the gap between 98% and 93% is entirely about human consistency.
Typical use at 93% means roughly seven pregnancies per hundred users over a year. For comparison, long-acting reversible methods such as IUDs and implants sit well under one, because they do not depend on daily behaviour.
That makes the honest question not whether the app works but how much a pregnancy right now would matter to you. If the answer is a great deal, the method is a poor match regardless of clearance.
It also offers no protection against sexually transmitted infections, which barrier methods do.
Where the method struggles
Basal temperature is sensitive to disruption. Poor sleep, alcohol, illness, fever and shift work all move the reading, and each disruption widens the fertile window the algorithm flags.
Irregular cycles produce more red days. Polycystic ovary syndrome in particular is associated with irregular or absent ovulation, which is precisely the population most likely to be reading a weight-loss site.
Rapid weight loss itself can disturb cycles temporarily, in either direction, which adds noise during exactly the period someone would be starting a GLP-1.
The daily commitment is real. A method requiring an action every morning fails in the way all such methods fail, which is what the typical-use figure measures.
What this is genuinely good at
Non-hormonal, which matters for people who cannot tolerate hormonal contraception or who prefer to avoid it, and it is reversible immediately.
It also works in reverse, identifying fertile days for people trying to conceive — though anyone on a GLP-1 should be discussing timing with a prescriber before that becomes relevant.
The data it produces about your own cycle is genuinely informative, and noticing a change in pattern is a legitimate reason to see a doctor.
The FDA clearance means the effectiveness claims were reviewed rather than asserted, which distinguishes it from cycle apps that make similar-sounding claims with no such basis.
Pros and Cons
Strengths
- Genuinely FDA-cleared as a contraceptive, unlike general cycle-tracking apps
- Non-hormonal and immediately reversible
- Published perfect-use and typical-use figures rather than one flattering number
- Works for conception planning as well
Drawbacks
- Typical use means roughly seven pregnancies per hundred users per year
- No protection against sexually transmitted infections
- Requires consistent daily measurement
- Disrupted sleep, shift work, alcohol and illness all degrade accuracy
- Irregular cycles produce many more fertile-flagged days
Who Should Pick It — and Who Shouldn't
Good fit
Someone with regular cycles and consistent sleep who wants a non-hormonal method and for whom a pregnancy would be unwelcome rather than catastrophic.
Look elsewhere
Anyone for whom avoiding pregnancy is critical, anyone with irregular cycles or shift work, and anyone on a GLP-1 who has not yet had the contraception conversation with their prescriber.
Frequently Asked Questions
Can a GLP-1 make me more fertile?
It can. Weight loss and improved insulin sensitivity can restore ovulation in people with polycystic ovary syndrome who were not ovulating regularly, which has produced unplanned pregnancies among people who believed conception was unlikely.
Does tirzepatide affect the pill?
Yes. Delayed gastric emptying can reduce absorption of oral contraceptives, and labelling advises a non-oral method or an added barrier method for four weeks after starting and after each dose increase.
Can I take a GLP-1 while pregnant or trying?
No. These medicines are not for use in pregnancy, and because semaglutide has a long half-life, labelling advises stopping at least two months before a planned pregnancy. Discuss timing with your prescriber.
How effective is Natural Cycles really?
The company publishes 98% with perfect use and 93% with typical use. Typical use is the number that matters — roughly seven pregnancies per hundred users per year, compared with well under one for IUDs and implants.
Considering Natural Cycles?
If you are on a GLP-1 and could become pregnant, talk to your prescriber about contraception this week. Fertility can change faster than people expect.
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Effectiveness figures and product model read from naturalcycles.com on August 25, 2026 and are the company's own published claims. Contraceptive and pregnancy guidance is from FDA-approved product labelling. This page is informational and not medical advice. Rx Saver Hub earns a commission on signups made through links on this page.