It can, and it should not. Declines and ratings for PrEP use have been publicly reported, with some carriers treating the prescription as a behavioural risk proxy. Practice varies, and several state regulators have pushed back on it.
This is one of the few genuinely contentious things in underwriting, and it is worth stating plainly.
What has been reported
Pre-exposure prophylaxis is a preventive medication taken by HIV-negative people to stay HIV-negative. It is highly effective, and by any straightforward reading it lowers the risk a carrier is pricing.
Some carriers have nonetheless treated a PrEP prescription as an indicator of higher-risk behaviour rather than as risk mitigation, and declines and ratings on that basis have been publicly reported. Insurance regulators in several states have challenged the practice, and some carriers have revised their guidance.
Practice varies between carriers, which is the operative fact. This is not a universal rule and it is not a settled one.
What this means practically
Do not stop taking a prescribed preventive medication in order to buy insurance. That trades a real health protection for a financial product, which is a bad exchange by any measure.
Do not conceal it either. Prescription data is checked, PrEP is visible in it, and a discrepancy between the application and the record is a far worse problem than the prescription.
What to do instead
Work with someone who knows which carriers currently handle PrEP sensibly, and treat a decline as information about that carrier rather than about you — the argument of applying after a decline. If you believe a decline was made on an improper basis, your state insurance department is the place to raise it.
The full treatment of this topic is on HIV.