If you're at least 65 years old or disabled — or have a loved one who is either — expect lots of action at the mailbox starting this month.

Resist the urge to throw out the mailings. After 18 months of a transitional drug-discount card, the biggest change to Medicare (search) in its 40-year history — the prescription drug benefit (search) known as Part D — is set to begin on Jan. 1. With the six-month enrollment period starting on Nov. 15, seniors will be deluged with insurers' marketing materials into next year.

The benefit addition will force many of the 42 million Medicare beneficiaries to compare their current drug coverage with the new plans and weigh which is best for their needs. The tradeoffs are complex and require close attention, Medicare analysts say.

"Rule No. 1 is don't rush" through the decision-making process, said Robert Hayes, president of the Medicare Rights Center, an independent, nonprofit national consumer service organization. "Promotional material is not educational material, so there will be spin and hucksterism."

There are 10 Medicare-approved insurance vendors selling drug plans nationally: Aetna (AET), Connecticut General Life Insurance, Coventry (CVH) , Medco (MHS) , MemberHealth Inc., PacifiCare (PHS) , Silverscript, UnitedHealthcare (UNH) , WellCare (WCG) and WellPoint. Some of the companies will place sales representatives at pharmacies to get the word out and sign up seniors.

Medicare's standard benefit, which companies may deviate from as long as they offer more and not less, is structured so enrollees pay a $250 deductible upfront before insurance kicks in, plus premiums ranging from about $20 to $37 a month. Beneficiaries are responsible for 25% of costs from $251 to $2,250. After that, the plan stops paying in the so-called doughnut hole, where enrollees pay for costs up to $5,100, after which time the government program picks up 95% of the tab.

What to do

Of all the considerations potential enrollees need to make, these are among the most important, according to experts:

Review what kind of drug coverage you have now, if any. Evaluate your income to determine what plans you can afford or if you are eligible for financial assistance. To receive federal help, a two-part means test is used limiting single participants to about $14,000 in annual income and $11,500 in property.

Don't be blinded by premium costs. A plan that offers a low monthly rate may have a large deductible, sizable copays or both.

Are the drugs you need most covered by the plan? If not, you likely will have to pay the full out-of-pocket cost unless you win an appeal. If your drugs are covered, what's the copay? Are they on the preferred list at the same dosages? Are there conditions? Ask about layered copays since some drugs can have copays of as much as $100, raising your out-of-pocket costs significantly. Mail-order options also can cut the tab.

Do the plans require step therapy, meaning you'll have to start with or switch to the lowest-cost drug first before trying more expensive ones?

Find out what pharmacy networks are part of the plans you're comparing. Are their drugstores accessible to you?

Ask how the appeals process works in case you need to argue that the plan cover a drug not on its preferred list.

Employer coverage, late penalties

If you have retiree drug coverage from your former employer or a union now, it's wise to find out if the plan will continue into next year.

If so, the employer needs to disclose whether its plan is considered as valuable as the Medicare drug benefit, which is worth about $1,400 in benefits, said Marilyn Moon, vice president and director of the health program at the American Institutes for Research, a nonprofit, nonpartisan think tank.

"Creditable" plans, including Veterans and those with Tricare, allow you to join Medicare Part D (search) at a later date without incurring a potentially substantial penalty for late enrollment. The penalty is 1% a month for the time you go without Medicare drug coverage after the enrollment period ends in May of 2006, she said. "If you wait five years, that would be a 60% penalty. Your premium would always be 60% higher."

On the market

At Aetna (AET) , potential enrollees can choose from three stand-alone drug plans with premiums ranging from $27.50 to $66.75 per month, said Frank McCauley, head of Aetna's retiree markets. One is equivalent to the Medicare benefit but offers copayments instead of coinsurance.

Aetna also offers a combination plan in 13 states for people who want to buy a more comprehensive plan that includes both the medical and pharmaceutical components, which can be cheaper, he said. "It will at times be less than what the stand-alone is in the market."

Aetna is working with CVS and Rite Aid to have kiosks and representatives available to answer customer questions about the Part D benefit, he said. The company has spent $50 million promoting its plans.

Seniors who enroll in Aetna's drug plans while taking a drug that's not on its accepted list will have 90 days to find a suitable covered replacement or lobby for its inclusion, McCauley said.

For example, if an older woman is taking cholesterol-lowering Crestor, which isn't on the list, the company will cover the drug for three months until she can switch to one that is covered, such as Lipitor, he said. "It's normally a very good time period to make that transition and holds the member harmless in terms of out-of-pocket costs."

Another health insurer, WellPoint (WLP) , also is offering a 90-day grace period starting the day a senior enrolls, said Susan Rawlings, president of senior services.

The company's three stand-alone plans vary: The lowest-cost one follows Medicare's basic structure with the $250 deductible, but instead of 25-75 coinsurance, it offers copays, she said. "We've converted that to copayments to make it easier to navigate."

Its lowest-cost plan includes a $5 copay for generic drugs and $25 for brand drugs, while subjecting more expensive injectable drugs to 25% coinsurance, Rawlings said.

By contrast, WellPoint's most comprehensive drug plan has no deductible, has more drugs on its approved list and offers generic coverage in the "doughnut hole" for $10 a prescription, Rawlings said.

Only a year commitment

For seniors who want to stay in traditional Medicare and have supplemental insurance known as Medigap, many will have three plans: Medicare, a Medicare supplemental policy and a new Part D drug plan, Moon said.

"What I recommend for those people who either don't like managed care or don't have access to good managed care in their area is that they do that even though they don't have much of an option," she said. "Take three plans."

Even if seniors choose a plan that displeases them initially, they have a chance to switch every year in an open enrollment process, Moon said. "The question is how many people who've gotten one, learned all the rules, are going to want to change midstream. Most of us are creatures of habit. You have to be convinced to change next time around."

Overall, most people will benefit by choosing a drug plan to add to their Medicare insurance, even if it's far from perfect, she said.

"What I would tell my mother if she was still alive is hold your nose and buy a plan," Moon said. "The government is still subsidizing a chunk of it. They're not great plans for the most part in terms of the way the coverage is designed, but they're certainly better than nothing for most people."