Many of the respondents are concerned by the side effects of their parents' medications (36 percent), the number of prescriptions they take (28 percent) and how long they've been taking the prescriptions (24 percent).

But it can get even dicier confronting an elderly parent about alcohol or illicit drug abuse, according to the report.

Nearly two-thirds (64 percent) of the respondents say they're less equipped to help their parents than their kids (36 percent) if they had a problem overusing drugs or alcohol. Those who live with their elderly parents are more likely to say they don't know how to talk to their parents about it than those who don't live with their parents (37 percent vs. 19 percent).

"The number of older Americans with substance use disorder is expected to rise from 2.8 million between 2002 and 2006 to 5.7 million by 2020, a situation for which adult children clearly are not prepared or well-equipped to handle," says Michael Polen, executive vice president, Medicare and operations, WellCare.

"While the sandwich generation understandably tends to focus on speaking with their teen children about the risks of substance abuse, it's apparent that it's equally important to have these conversations with parents as well," Polen says.

Respondents cite a number of reasons for not wanting to engage in that discussion: they think their parents would get mad at them (22 percent), they wouldn't know how to start the conversation (20 percent), or they don't feel like they're in a position to tell them they have a problem (18 percent).

More than 1 in 10 (11 percent) say they've talked to them in the past but it didn't go well — that number jumps to 20 percent for those who live with their parents.

Many adult children are in the dark when it comes to their parents' use of drugs and alcohol, according to the report. Three-quarters (75 percent) admit that it's possible to mistake potential signs of overuse, misuse and abuse of prescription drugs or alcohol for normal behaviors of aging. Those who live with their parents are more likely than those who don't to say it's possible to mistake the signs (83 percent vs. 74 percent).

"There are numerous factors that can lead seniors down a path to substance abuse or misuse, ranging from loneliness to availability of multiple prescription drugs to depression," says Kevin Middleton, WellCare's vice president, behavioral health programs.

"Oftentimes, those who are closest may in fact be in the dark about the signs, which is why it's important to check in, check up and be informed about the symptoms of abuse," Middleton says.