One of the fiercest fights happening within the Republican Party right now is what to do about Obamacare’s Medicaid expansion.

The Affordable Care Act broadened Medicaid eligibility to cover millions more low-income Americans, and offered states federal money to recoup the costs.

But only 16 states with Republican governors expanded Medicaid, including Ohio’s John Kasich, who is among a group of state leaders lobbying for continuing expansion. Seventeen governors rejected the option, though, often with the justification that Medicaid doesn’t actually improve people’s health.

So does it? With more than 10 million people who gained coverage through Medicaid expansion, and the newest Republican Obamacare replacement plan threatening to end the program in 2020, the question seems worth parsing.

We actually have some pretty good data out of Oregon about Medicaid’s effects on health. There, researchers from Harvard tracked what happened to the winners and losers of a state lottery that offered Medicaid to 10,000 randomly selected Oregonians in 2008. This is the closest we have to a randomized trial on health insurance — the gold-standard study methodology — so it’s been a treasure trove of information for researchers. The study also gives us a pretty good picture of how exactly Medicaid impacts people’s health — and where it falls short.

Medicaid improves people’s well-being, but it’s not perfect

In Oregon, people who gained Medicaid reported improvements on a number of important outcomes after two years on the program. Here’s where Medicaid clearly helped:

Medicaid coverage led to a massive reduction in the risk of depression. Thirty percent of patients in the control group (who didn’t gain Medicaid access) screened positively for depression two years after the state lottery. Among the people who got Medicaid, that number dropped by a third (or 9 percentage points). And we know depression is one of the leading causes of disability in the country, so that impact is a big deal.

Thirty percent of patients in the control group (who didn’t gain Medicaid access) screened positively for depression two years after the state lottery. Among the people who got Medicaid, that number dropped by a third (or 9 percentage points). And we know depression is one of the leading causes of disability in the country, so that impact is a big deal. People reported better overall health. Participants were asked whether they thought their health improved after they gained Medicaid access. They did. “Medicaid coverage led to an increase in the proportion of people who reported that their health was the same or better as compared with their health 1 year previously,” the study authors reported — a difference of about 8 percentage points compared with the control group.

Participants were asked whether they thought their health improved after they gained Medicaid access. They did. “Medicaid coverage led to an increase in the proportion of people who reported that their health was the same or better as compared with their health 1 year previously,” the study authors reported — a difference of about 8 percentage points compared with the control group. Medicaid increased health care access. When people gain Medicaid, they use more health care — of just about every kind you can think of. They use more prescription drugs, see the doctor more often, get more mammograms, Pap smears, and PSA tests, and the list goes on. (This is consistent with other studies that find emergency department and primary care use goes up with Medicaid expansion, and people report better access to medicines.)

When people gain Medicaid, they use more health care — of just about every kind you can think of. They use more prescription drugs, see the doctor more often, get more mammograms, Pap smears, and PSA tests, and the list goes on. (This is consistent with other studies that find emergency department and primary care use goes up with Medicaid expansion, and people report better access to medicines.) Gaining health insurance reduced financial strain. The researchers asked participants for information about a number of financial measures — out-of-pocket spending on health care, medical debt — and on all these measures, too, gaining Medicaid helped people. In particular, catastrophic expenditures — or out-of-pocket medical expenses that exceeded 30 percent of income — were nearly eliminated. There was a 25 percent drop in having a bill sent to collections. (This squares with an NBER paper on credit report data that found less financial stress in states that expanded Medicaid.)

The researchers asked participants for information about a number of financial measures — out-of-pocket spending on health care, medical debt — and on all these measures, too, gaining Medicaid helped people. In particular, catastrophic expenditures — or out-of-pocket medical expenses that exceeded 30 percent of income — were nearly eliminated. There was a 25 percent drop in having a bill sent to collections. (This squares with an NBER paper on credit report data that found less financial stress in states that expanded Medicaid.) Medicaid improved diabetes care. Researchers found that people who gained Medicaid had a greater probability of getting diagnosed with diabetes (3.83 percentage points) and using medications for diabetes (5.43 percentage points) compared with the control group, which did not get Medicaid.

But it didn’t help on every measure the researchers looked at, which is why I came away from reading this study thinking Medicaid is necessary but not sufficient for improving health. Here’s where Medicaid was less helpful:

Medicaid did not improve blood sugar control. The researchers found no effect on a common measure of diabetes control called HbA1c two years after getting Medicaid. So while more people were diagnosed, and more gained access to medications, their health didn’t actually improve by this measure.

The researchers found no effect on a common measure of diabetes control called HbA1c two years after getting Medicaid. So while more people were diagnosed, and more gained access to medications, their health didn’t actually improve by this measure. Medicaid coverage also didn’t have an effect on the prevalence or diagnosis of high blood pressure or high cholesterol, or on the use of medications for these conditions. People were no more likely to be taking a medication for high blood pressure or cholesterol, and cholesterol and blood pressure levels were not detectably better in the people who gained Medicaid.

This last point squares with another 2016 study in the Annals of Internal Medicine that found low-income folks in states that expanded Medicaid were more likely to be diagnosed with diabetes and high cholesterol — though not high blood pressure. Yet this 2017 Health Affairs study found an association between Medicaid expansion and improved high blood pressure control.

Medicaid improves people’s well-being — but it’s not perfect

You might say the Oregon experiment, while very robust, isn’t the final word on Medicaid’s effects on health.

Or you could argue that if the researchers chose to look at different end points, they might have found greater improvements.

Or you can read the Oregon study — as some have — as an indictment of Medicaid, since the people who gained health coverage didn’t seem to improve their health on the hard clinical measures (like blood glucose and blood pressure).

I think that last reading is probably wrong. It’s clear people who gain Medicaid are better off than those who don’t. The program improved their access to care, made them less depressed, reduced their financial strain, and improved their perceptions of their health and well being — all measures that are likely to improve their overall health and reduce their mortality risk in the long run. (Other researchers have found Medicaid expansion has likely averted tens of thousands of deaths each year.)

Still, Medicaid isn’t perfect. “Access to the health system [through Medicaid] improves your health and well-being substantially while not being sufficient to control diabetes and high cholesterol,” said lead study author Katherine Baicker, a health economist at the Harvard T.H. Chan School of Public Health.

That’s not so different from people on other types of insurance, she pointed out. “There’s lots of evidence throughout the health care system that we don’t do a great job at managing chronic health conditions in general. And Medicaid doesn’t seem like the magic bullet on that.”

Now it’s up to policymakers to decide how to fund a program that American lives depend on.