WASHINGTON (CNN) -- An alarming number of women over the age of 59 are suffering from substance abuse and addiction, according to a two-year-long study released Thursday by the National Center on Addiction and Substance Abuse.

Of 25.6 million American women over the age of 59, the report said 4.4 million (17 percent) are addicted to nicotine, approximately 1.8 million (7 percent) abuse alcohol, and 2.8 million (11 percent) abuse prescription psychoactive drugs.

Illegal drugs, however, do not play a major role with mature women; only 3.8 percent say they have tried illegal drugs.

Not only are mature women at a higher risk to become addicted faster, but physicians are slow to even consider a substance abuse diagnosis when treating these women, the study said.

Many physicians inadvertently exacerbate abuse problems because of inappropriate treatment. For example, the study found that many physicians will diagnose depression and treat it with anti-depressants when the real problem is alcohol abuse. Some anti-depressants are known to enhance the effects of alcohol.

Joseph Califano, chairman and president of the center, surmises that shame and denial have a large role in the "epidemic levels" of abuse and addiction in these women.

Prevention strategies, says the report, must educate mature women and their friends, family and caregivers about the risks of abuse, so if these problems arise they are identified as early as possible. Other strategies mentioned in the report include: educating physicians regarding diagnoses and treatment; using pharmacist and nursing home expertise to eliminate inappropriate prescriptions; and establishing social and mental health programs to counsel and support mature women.

The report was funded by Bristol-Myers Squibb Foundation, Inc.