“You can't get pregnant while on a GLP-1.”
What the evidence shows
These drugs are not contraceptives, and unplanned pregnancies on them are common enough to have earned a nickname. Two mechanisms stack. First, weight loss can restore ovulation in people who weren't ovulating because of obesity or PCOS — someone who assumed she couldn't easily conceive may suddenly be fertile again while using the same casual or no contraception. Second, for tirzepatide specifically, oral birth-control pills can become less reliable because the drug slows stomach emptying. Enough people conceive on these medicines that researchers now study first-trimester exposure outcomes.
What we still don’t know
There's no reliable count of how many pregnancies these drugs have 'caused,' so anyone quoting a hard number is outrunning the data — the phenomenon is well grounded mechanistically but not precisely quantified. It also varies by person: not everyone regains fertility, and the degree of contraceptive interaction (tirzepatide only) depends on the method used.
Why the claim misleads
'You can't get pregnant on it' is a dangerous assumption, because the surprise cuts exactly the wrong way: people who don't want to conceive can become newly fertile without realizing it, on a medicine that is not recommended in pregnancy. That's precisely why the contraception-and-conception conversation belongs at the start of treatment, with a clinician, not after a positive test.
Graded by The Peptide Era · evidence, not hype