Google doesn't even use Gmail data to target ads. It strains credulity to believe they'd use medical data to do so, even assuming that is legal.
...Anymore. They did exactly this from basically launch up to 2017, and they only stopped because it was scaring corporate customers away from buying GSuite. https://www.theverge.com/2017/6/23/15862492/google-gmail-adv...
https://www.google.com/amp/s/www.nytimes.com/2017/06/23/tech...