Enrollment for Medicare 2009 started Saturday. People 65 years of age or older who did not sign up for the federal drug benefits can enroll until the end of 2008.

Several advocacy groups are strongly advising everyone to be very careful when they take their options because several popular plans are raising monthly premiums or changing benefits.

“[People] should not assume their plans will remain the same in 2009," said Robert Hayes, president of the Medicare Rights Center.

This is Medicare’s fourth year and the popular federal program will suffer some changes. Costs will grow for seniors. The average premium will be up by 25 percent. Several plans are also changing the covered prescriptions and some of them their names.

Seniors are advised to call their plans and find out whether the lists of covered medications were changed or not, the Medicare Rights Center said. They are also advised to ask about the drug co-payments, the pharmacies in the network and whether there are any restrictions on the medications.

"Our message is more critical this year than any past years," said Julie Brookhart of the Centers for Medicare and Medicaid Services.

"It is our motto: ‘Plans change, you change. Shop and compare,’ "she added.

For more information on the Medicare drug benefits and the different types of plans available visit www.medicareinteractive.org, www.medicare.gov or call 800-633-4227.

It is important to compare the costs of the popular plans, but keep in mind that the cheapest one may have restrictions.