Open enrollment is here—the time of year when you can sign up or change your 2017 health insurance.

For many individual and family health plans—including those purchased through the Affordable Care Act—open enrollment runs through Jan. 31.

If you are covered by Medicare, Dec. 7 marks the end of open enrollment. During that time, you can switch from original Medicare to a Medicare Advantage plan (the private managed-care version of Medicare), or vice versa. You also can replace one Medicare Advantage plan with another, or change your Medicare Part D (prescription drug) plan.

But when do you really need to change health insurance plans? Here, four instances where you either have no choice or should consider alternatives:

Your Doctor Stops Accepting Your Insurance

It’s good for your health to work with healthcare providers you trust, according to research.

For example, a 2014 PLOS One analysis of 13 studies found that a positive doctor-patient relationship can make a real difference for conditions such as asthma, obesity, and osteoarthritis pain.

But right now, provider lists are in flux at a number of health insurers, so you can’t assume that the doctors you prefer who currently take your insurance will do so in 2017.

What to do Contact the billing departments of the healthcare providers you want to see and make sure they will continue to accept the specific insurance product you now have.

Check with your preferred hospital as well and confirm with your insurer.

If key healthcare providers are not on the 2017 list for your insurer, you may need to ask which insurance products they will accept in 2017 and consider a new plan.

Your Premiums Are Going Up, Up, Up

Insurance premiums for 2017 plans purchased through state and federal marketplaces may see bigger increases than in recent years, a Kaiser Family Foundation analysis shows.

Most people who buy ACA plans will be somewhat shielded from increases because they’ll get a tax credit to offset premium costs.

What to do Think about what you really need and don’t automatically rush out to buy the cheapest plan. Those plans may cost more in the long run. That's because they often come with:

*Higher deductibles—the amount of money you have to spend before insurance kicks in.

*Higher co-pays—the flat amount you pay every time you visit a doctor, hospital, or other healthcare provider.

*Steeper coinsurance—the portion of the bill you have to pay even after you meet your deductible.

Those out-of-pocket expenses, which can run into thousands of dollars, may tempt you to delay needed care.

In addition, some of the lower-cost plans have smaller networks of doctors, limiting your choice of providers.

Your Medication Costs Are Skyrocketing

Every insurance plan that offers prescription drug benefits has a formulary, or a list of medications it covers, at least in part.

Each medication in a formulary is usually placed in a tier that determines your out-of-pocket cost.

For tier 1 medications, which are usually generic, you may pay only a few dollars. As the tier numbers go up, so does the amount you pay.

What to do Formularies often change year to year, so check with your plan to make sure it’s not removing a medication you take regularly from its covered list.

If it is, you may need to investigate the formularies of other insurance companies.

But first, file an appeal with your current insurer or ask your doctor to switch you to a covered medication with similar benefits.

If you take multiple high-tier medications, cost-cutting tips from Consumer Reports' Best Buy Drugs experts can help you reduce your out-of-pocket expenses.

Your Plan Is Not Available Anymore

In some cases, you may be forced to change health insurance plans.

For example, Aetna, Humana, and United Healthcare have announced that they are dropping out of many ACA state marketplaces, citing financial losses.

What to do Check out our comprehensive insurance buying advice.