But it’s crazy to say that antibiotics were the “cause” of the failure in that case. It’s like saying, if you stay out late one night drinking, and miss your pill the next morning because you overslept, that alcohol “caused” your OCP to fail. Not taking your pill caused your OCP to fail.
But then, I’m the kind of pill taker who has never (in 10 years) “just not felt like” taking my pills on time. In general, I “just don’t feel like” getting pregnant a hell of a lot more. I think the most I’ve been late is 12 hours , and I’ve never erred twice in a cycle, ever.
One might expect to see a decline in fertility and frequency of sex due to illness. A UTI, sinus infection, etc. can certainly put someone off their game. If we assume illness correlates with antibiotic use, we would then expect the OCP+antibiotic pregnancy rate to be lower than the OCP only rate. If the rates are equal, that *could *indicate reduced effectiveness of the pill. I wonder if studies take that into account?