I think you could solve quite a bit of it just by writing your own CAPTCHA (instead of using a public one that there's already exploit code for.) There's a PyGimp script you can tweak here:
Given the stuff that ends up in my spam buckets, I'd tend to expect that anything involving medication or health care is one of the "more valuable targets", at least from the set of things that have CAPTCHAs as a significant obstacle.
https://spideroak.com/code
Won't stop the people who proxy your CAPTCHA on another site, but the people doing that probably have more valuable targets.