Volunteer Tony Hausner, left, assists an enrollee arriving to a health insurance education and enrollment event in Silver Spring on Saturday. (Andrew Harrer/Bloomberg)

I’m trying to decide among a few plans on the exchange. How do I know which ones cover prescription drugs?

All of them should. In the past, some individual policies offered drug coverage as an option for an additional cost, but that will change on Jan. 1. Prescription drug coverage is one of the 10 essential benefits under the Affordable Care Act, and all health insurance plans will be required to cover at least one drug in every category and class in the U.S. Pharmacopeia, the official list of approved medicines.

That makes things easier, but how do I find out whether the medicines I’m taking are covered?

You should request a copy of the plan’s drug formulary, or preferred-drug list, which tells you what’s covered. On the federal exchange, you may be able to find this when you click on the “details” button for a specific plan. Your co-pay or co-insurance — the amount that you’re responsible for — could vary enormously. Some plans may ask you to pay $30 for a medicine while others could charge you $1,000 for the exact same thing, so be sure to check the name of the drug and the specific dosage you need. Don’t forget to find out whether the plan covers the number of monthly doses needed. If you are taking medication for a chronic condition or something that has a high retail price, you may want to ask whether your plan maintains a separate list of specialty pharmaceuticals that are covered. You should keep in mind that the formularies are constantly in flux, and right now more than usual. For some plans on the exchange, the drug formularies are a work in progress as medical and patient advocacy groups continue to press insurers to add certain medications they think are important to cover.

I found the drug formularies, but I’m having trouble understanding what everything means.

The drug lists are often divided into tiers, and each tier has different reimbursement levels. For many plans, Tier 1 drugs are the cheapest and usually include generics. The higher the tier number, the higher the co-pay or co-insurance. You should pay attention to a few other things, including whether the drug requires authorization under certain plans. This could be time-consuming and means you’re not guaranteed access to the medication. Also, you should find out whether there is any “step” requirement — meaning that your doctor may have to try a different drug first and provide documentation that it failed before the insurer will cover another medicine.

What if a drug I take is not on the list?

Your doctor can ask for an exception for medical need so that the insurer will cover it. The Centers for Medicare and Medicaid Services is encouraging insurers to respond to such requests within three days. If your request is denied, you can go through your state’s appeals process, which usually is handled by insurance regulators. If you still can’t get coverage and need to take the drug, you’ll have to bear the full cost out of pocket, as it won’t count toward your deductible or your co-insurance maximum.

What if my medication is covered but I can’t afford the co-pay or co-insurance?

If you have a chronic illness, some foundations offer assistance to those with financial need. Pharmaceutical companies also sometimes offer discount cards or rebates. You may want to consider contacting a patient advocacy group to learn more about what help is available.