Baby boomers seeking mental-health care are getting an unpleasant surprise when they turn 65: Finding a therapist who takes Medicare can be harder than finding one who takes private insurance.

That discovery came as a jolt to Janis Zimmermann. Ms. Zimmermann, 69 years old, had a long relationship with her psychologist. She hadn’t seen her for several years when she made an appointment last year seeking help to cope with the stress of caring for her disabled partner and her elderly parents. When Ms. Zimmermann, who retired...

Baby boomers seeking mental-health care are getting an unpleasant surprise when they turn 65: Finding a therapist who takes Medicare can be harder than finding one who takes private insurance.

That discovery came as a jolt to Janis Zimmermann. Ms. Zimmermann, 69 years old, had a long relationship with her psychologist. She hadn’t seen her for several years when she made an appointment last year seeking help to cope with the stress of caring for her disabled partner and her elderly parents. When Ms. Zimmermann, who retired from a job in land protection in Madison, Wis., arrived at her appointment, she was told that her therapist didn’t accept Medicare.

Ms. Zimmermann, who’d had to pay the psychologist a small copay when she had private insurance through her job, paid $190 out of pocket for the session. She hasn’t been back to therapy since, though her stress and worries haven’t gone away.

“I feel very isolated. I’ve just been dealing with all the stuff on a day-to-day basis,” she says.

Surging demand for mental health care has made it difficult for many people to find therapists, particularly those who will accept their insurance. The task is even tougher for many baby boomers, therapists say, because many psychologists, psychiatrists and social workers—even those who participate with private insurance plans—don’t take Medicare.

Baby boomers were the first generation to embrace therapy in significant numbers, notes Vaile Wright, senior director of healthcare innovation at the American Psychological Association. In the 1950s and 1960s, new approaches like cognitive behavioral therapy were developed that generally took less time—and were more accessible—than the then-popular psychoanalysis that often demanded years of intensive treatment. As baby boomers aged, the number of mental-health professionals grew dramatically.

Why many therapists don’t participate in Medicare

The reasons therapists decide not to participate in Medicare are similar to why some don’t take private insurance plans either: Therapists say reimbursement rates are too low and the paperwork is arduous. Medicare pays about $103 for a 45-minute individual therapy session with a clinical psychologist and about $77 for one with a licensed clinical social worker, according to the federal Centers for Medicare & Medicaid Services.

The going rate for a session with an experienced clinical psychologist can be as much as $300. The typical fee for a session with a licensed clinical social worker costs between $120 and $180, says Anna Mangum, deputy director of programs at the National Association of Social Workers.

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There are additional obstacles for Medicare patients. Many people with private insurance have out-of-network benefits, allowing them some reimbursement when they see therapists who don’t take insurance. Medicare limits what its participating providers can charge and doesn’t allow practitioners to bill patients for the difference between its cap and their typical fee. Many psychologists opt out of Medicare as a result, says Stephen Gillaspy,

senior director of health and healthcare finance at the American Psychological Association. Medicare patients who want to see therapists who don’t participate in the program generally have to pay the full rate.

Ms. Zimmermann says she would happily pay the difference between what Medicare covers and the $190 her therapist charges for a session if it were allowed. “I really don’t want to go see anybody else,” she says.

Medicare also doesn’t cover most services of entire groups of mental-health providers, including licensed professional counselors. Legislation has been introduced in Congress that would allow counselors to participate in and directly bill Medicare.

The Centers for Medicare & Medicaid Services says that it has taken several actions to increase access to mental-health care for Medicare patients during the pandemic, including allowing them to receive therapy by phone. CMS didn’t respond to requests for comment on therapists’ complaints about reimbursement and administrative issues.

Challenges with Medicare patients

Treating Medicare patients can be complicated, says

Robert Trestman, a psychiatrist at the Carilion Clinic in Virginia and chair of the American Psychiatric Association’s Council on Healthcare Systems and Financing.

“When I’m seeing patients who are 70 years old, they are typically on a dozen medications. It’s not unusual for me to talk to an endocrinologist, a primary-care doctor and a rheumatologist for a single patient and a lot of that is uncompensated time,” says Dr. Trestman, who treats Medicare patients. The combination of low reimbursement and high complexity pushes some psychiatrists to opt out of the program, he says.

Demand at Carilion’s outpatient clinic has soared during the pandemic: The waitlist for new patient appointments for psychiatric care numbers 800 people, Dr. Trestman says. About one-third of those patients are on Medicare.

About 55% of U.S. psychiatrists accepted Medicare in 2009-2010, according to a study published in 2014 in JAMA Psychiatry that used data collected by the Centers for Disease Control and Prevention. About 86% of physicians in other specialties took Medicare. Dr. Trestman says he believes those numbers are similar now.

People enrolled in Medicare Advantage plans administered by commercial insurers often face narrow networks of providers. In 2014, about 30% of psychotherapy services received by Medicare Advantage members were out of network, according to a study published in 2019 in the journal Health Affairs.

Jessica Koblenz, a clinical psychologist in New York City, recently looked into taking Medicare after receiving several calls from Medicare patients looking for treatment. Colleagues told her about long waits for payments and difficulties in fixing errors. And the reimbursement rates “were nowhere near what I would find worthwhile,” said Dr. Koblenz, who specializes in treating trauma and bereavement.

“It’s a shame because there’s such a need,” she says.

What Medicare patients can do

Therapists suggest making plans for mental-health care months before your 65th birthday. If your current therapist doesn’t take Medicare, ask them to consider enrolling in the program so you can continue treatment. Or you can transition to a therapist who does accept it.

Matt W. Wolff, a licensed professional counselor in McKinney, Texas, says he starts working with clients several months before they enroll in Medicare to find them a psychologist or social worker who can bill the program. He also keeps three slots in his weekly schedule for long-time clients who have transitioned to Medicare. He works with them for free until they can wrap up treatment.

Many therapists have sliding scales, so out-of-pocket costs could be lower. And telehealth can give you access to a larger pool of providers, including therapists who are far away from you. Larger practices and hospital-based clinics are more likely to accept Medicare, says Dr. Trestman.

It is also worth looking into what are known as collaborative care practices. These practices, which are growing in number, incorporate treatment from psychiatrists, psychologists and social workers into primary care. They often take all kinds of insurance, including Medicare.

Write to Andrea Petersen at andrea.petersen@wsj.com