Granted, no parent is perfect. And whining about parental failure, real or not, is practically an American pastime that keeps the therapeutic community dutifully employed.

But just as there are ordinary good-enough parents who mysteriously produce a difficult child, there are some decent people who have the misfortune of having a truly toxic parent.

A patient of mine, a lovely woman in her 60s whom I treated for depression, recently asked my advice about how to deal with her aging mother.

“She’s always been extremely abusive of me and my siblings,” she said, as I recall. “Once, on my birthday, she left me a message wishing that I get a disease. Can you believe it?”

Over the years, she had tried to have a relationship with her mother, but the encounters were always painful and upsetting; her mother remained harshly critical and demeaning.

Whether her mother was mentally ill, just plain mean or both was unclear, but there was no question that my patient had decided long ago that the only way to deal with her mother was to avoid her at all costs.

Now that her mother was approaching death, she was torn about yet another effort at reconciliation. “I feel I should try,” my patient told me, “but I know she’ll be awful to me.”

Should she visit and perhaps forgive her mother, or protect herself and live with a sense of guilt, however unjustified? Tough call, and clearly not mine to make.

But it did make me wonder about how therapists deal with adult patients who have toxic parents.

The topic gets little, if any, attention in standard textbooks or in the psychiatric literature, perhaps reflecting the common and mistaken notion that adults, unlike children and the elderly, are not vulnerable to such emotional abuse.

All too often, I think, therapists have a bias to salvage relationships, even those that might be harmful to a patient. Instead, it is crucial to be open-minded and to consider whether maintaining the relationship is really healthy and desirable.

Likewise, the assumption that parents are predisposed to love their children unconditionally and protect them from harm is not universally true. I remember one patient, a man in his mid-20s, who came to me for depression and rock-bottom self-esteem.

It didn’t take long to find out why. He had recently come out as gay to his devoutly religious parents, who responded by disowning him. It gets worse: at a subsequent family dinner, his father took him aside and told him it would have been better if he, rather than his younger brother, had died in a car accident several years earlier.

Though terribly hurt and angry, this young man still hoped he could get his parents to accept his sexuality and asked me to meet with the three of them.

The session did not go well. The parents insisted that his “lifestyle” was a grave sin, incompatible with their deeply held religious beliefs. When I tried to explain that the scientific consensus was that he had no more choice about his sexual orientation than the color of his eyes, they were unmoved. They simply could not accept him as he was.

I was stunned by their implacable hostility and convinced that they were a psychological menace to my patient. As such, I had to do something I have never contemplated before in treatment.

At the next session I suggested that for his psychological well-being he might consider, at least for now, forgoing a relationship with his parents.

I felt this was a drastic measure, akin to amputating a gangrenous limb to save a patient’s life. My patient could not escape all the negative feelings and thoughts about himself that he had internalized from his parents. But at least I could protect him from even more psychological harm.

Easier said than done. He accepted my suggestion with sad resignation, though he did make a few efforts to contact them over the next year. They never responded.

Of course, relationships are rarely all good or bad; even the most abusive parents can sometimes be loving, which is why severing a bond should be a tough, and rare, decision.

Dr. Judith Lewis Herman, a trauma expert who is a clinical professor of psychiatry at Harvard Medical School, said she tried to empower patients to take action to protect themselves without giving direct advice.

“Sometimes we consider a paradoxical intervention and say to a patient, ‘I really admire your loyalty to your parents — even at the expense of failing to protect yourself in any way from harm,’ ” Dr. Herman told me in an interview.

The hope is that patients come to see the psychological cost of a harmful relationship and act to change it.

Eventually, my patient made a full recovery from his depression and started dating, though his parents’ absence in his life was never far from his thoughts.

No wonder. Research on early attachment, both in humans and in nonhuman primates, shows that we are hard-wired for bonding — even to those who aren’t very nice to us.

We also know that although prolonged childhood trauma can be toxic to the brain, adults retain the ability later in life to rewire their brains by new experience, including therapy and psychotropic medication.

For example, prolonged stress can kill cells in the hippocampus, a brain area critical for memory. The good news is that adults are able to grow new neurons in this area in the course of normal development. Also, antidepressants encourage the development of new cells in the hippocampus.

It is no stretch, then, to say that having a toxic parent may be harmful to a child’s brain, let alone his feelings. But that damage need not be written in stone.

Of course, we cannot undo history with therapy. But we can help mend brains and minds by removing or reducing stress.

Sometimes, as drastic as it sounds, that means letting go of a toxic parent.