Can preventative medicine help get our rising medical expenses under control? Does it save money when people get an annual physical? Other preventative treatments? Or would it be better if people just go to the hospital when they're sick or in pain? What's going to cost less over the long term? That is, does preventative care decrease total medical spending?
Hearing things like "an ounce of prevention is worth a pound of cure", suggesting that you do much better to "nip things in the bud", I would have thought yes. When I wrote about how health insurance is weird because we have the idea that people should not be charged in proportion to their risk we had some discussion in the comments over how preventative care affected costs, so I decided to look into it.
The best source I could find on this was a "research synthesis report" by Joshua Cohen and Peter Neumann of Tufts Medical Center: The cost savings and cost-effectiveness of clinical preventive care (2009). There are a lot of subtleties here, and it looks like they dealt with them well.
They broke interventions down into "cost saving", "good value" , and "expensive". They only found two that they were convinced were cost saving: counseling older adults to take low-dose asprin and giving kids standard childhood immunizations. The "good value" ones may still be worthwhile preventive care in that they provide good heath benefits for a relatively small increase in medical costs, but they do not "save money" in the sense that per-person medical expenses would go down if we deployed them more widely.
They don't look at all interventions, and the one I most wanted to see, the annual physical, is not in there.  It looks like that's because it's more of a package of interventions than anything else. Should we abandon the periodic health examination? NO (2009), argues that the annual physical is worthwhile primarily because "we can piggyback much-needed preventive care onto these visits". But if the preventative care isn't really "much-needed", then I would think the annual physical wouldn't be either.
It looks like we shouldn't be encouraging people to go to the doctor every year even if they feel fine.
 Meaning cost of no more than $100K per additional Quality Adjusted Life Year (QALY). It's always shocking to see $/QALYs in the range of $100K as "cost effective" when deworming has a $/DALY (which is basically the same as $/QALY in this context) somewhere in the $100 range. Once of GiveWell's top charities, SCI, works in deworming.
 I did find a different study, Preventive Health Examinations and Preventive Gynecological Examinations in the United States, but while they find that physicals tend to lead to lots of unneeded tests and say that "some observers have raised concerns that preventive visits are an inefficient use of physicians' time, potentially interfering with timely access for sick patients" they don't have a reasoned stand for or against them. They do cite a 1979 Canadian Task Force Report that recommended against a yearly well visit and instead suggested "a selective plan of health protection packages appropriate to the various health needs at the different stages of human life", which they don't define well. I think it means visits every few years, but how far apart depending on the age of the patient. Still, it's really unlikely things haven't changed since 1979. They also cite a 1981 American College of Physicians guide, who's abstract declares that "present data are not adequate evidence justifying annual complete examination of the asymptomatic patient at low medical risk", but it's paywalled. This is a case where I findit strange that the papers that continue to be most cited are decades old.