If my mom is on Medicaid and also has Medicare and a doctor said he does not take medicaid, is the Medicare different?

So, Bunky, maybe one could look at it this way:
Your Mom is also under contract, as well as the doctor to Medicaid.

Just Medicare is different, but the "HMO" type agreement with Medicaid requires the patient to see a Medicaid contracted doctor. Otherwise, it would be called "out of network" (a term used by insurance companies) and not be covered by Medicaid, or even by the Medicare portion, imo.

There are ways around this, however I don't know if it will benefit your Mom.
She can sign up for STAND ALONE MEDICARE, and the MEDI-CAL portion would be separate. With Stand-alone, one can see the doctor of their choice, have it covered, would not need to even obtain prior authorization by Medicare.
There is one caveat: Medicare will chop up the doctor's bill so harshly that it will seem like punishment and it will interfere with the doctor/patient relationship.

I am going to stop now, because I doubt that I am qualified to answer any questions that may arise out of me sharing my limited knowledge and opinions.

Get your Mom the best medical treatment available and deal with the rest later.

In other words, Jeanne Gibbs is right.

As well as others posting here.

There are complications with Medicaid.
How to explain this?
The primary insurance is Medicare.

A doctor can be contracted with Medicare, and must accept what Medicare allows as payment, the 80% is paid by Medicare, the 20% by the patient (but if dr. bills $100, and Medicare only 'allows' $45, and Medicare pays 80% of that, the patient pays only the 20% of the $45. These are the rules. Many don't know that, don't understand that, and others just don't go by the rules.

A doctor "Not contracted with Medicare" may see you, receive payment from Medicare as a courtesy, and bill the entire balance to the patient. Or, at least 20 years ago the doctor could do this. Medicare might have put a stop to this independent practice, as evidenced by the many private practice physicians no longer accepting Medicare at all.

When the low-income Medi-Cal (=Medicaid) is the secondary insurance payor, the doctor who "accepts" Medicaid is contracted by Medicare and Medi-Cal and is required by contract and by law to accept the low payments. One cannot make a separate agreement with the patient to receive more than the contracted amount.
It is the law.
If a patient is on Medicaid and wants insurance to cover their visit, they must see a Medicaid contracted doctor. Otherwise, one might as well be rich and be paying privately to see a doctor. If that were possible, it begs the question, why is the person on Medicaid, and how was it that they qualified?

It is still my hope that someone will somehow find a legal and equitable way someday to be seen by a real doctor OF THEIR CHOICE and have some kind of real help paying for it someway. Taking billions of healthcare dollars away from physicians and paying those funds to the insurance industry will never be the answer, imo.

Any doctor can refuse to accept any insurance. Some do not accept Medicare. Many reject Medicaid. In general, large practices with patients on a variety of insurance plans can best afford to absorb the lower payments from these sources.

I was looking for a geriatric psychiatrist and had a nice list of doctors to call. Not one of them accepted Medicare. Sigh.

We may have awesome quality medical care in this country, but we have a piss-poor way of paying for it!

For doctors visits, Original Medicare's Part B pays for the doctor at roughly 80% of whatever Medicare contracts indicate for your region. So the remaining 20% will need to be paid. Usually those on Medicare have a secondary insurance policy, like maybe Humana, United, Blue Cross. If the doctor participates with the secondary insurer, then the secondary get billed the 20% at whatever rates that insurer has negotiated with the provider. If your secondary has a co-pay, you would need to pay the co-pay at the time of service or maybe even at the time of the appointment.

But some folks are Dual-Eligible's which means they are on Medicare & Medicaid -
usually with Medicare as the primary and Medicaid as the secondary. Now both have pre-set fixed prices for services. Medicaid is very, very low payments, so many doctors won't accept dual-eligibles.

Some folks do not have any secondary insurer. The doctor can require you to do whatever private pay rate for the 20% & it could be in advance.

My mom for decades had Medicare and a high option Blue Cross. Zero copay no matter what. When she went into a NH and onto Medicaid, her Blue Cross was "suspended" (they won't pay if there is another insurer). Medicaid became her secondary or sometimes her primary insurer. But before going into the NH, she had eye surgery and needed a follow-up done a few months into living at the NH; the opthamalogist did see her at his office but she paid the co-pay directly. I mention this cause if your mom really, really likes this doc and has a history of care & relationship with them; and if they won't take Medicaid, it could be well worth asking if mom can be seen and private paying the 20% if you / she can afford to do so. Btw he discounted it too! My point is to ask if there are any options to pay.

Medicare is paid by your Mom out of her social security, and out of payroll taxes back when she was working, It is under the umbrella of the Federal government.

Medicaid is under the umbrella of the State and is funded through all the taxpayers in your Mom's State. The Federal government also helps the State with some funding. Medicaid is for those who are at or below poverty level. Not sure how it works for secondary insurance.

Sounds like your Mom had Medicare as her primary health care, and Medicaid as her secondary health care. Not all doctors will take both, or just Medicaid.