Jessica McCabe, creator of the YouTube channel “How To A.D.H.D.,” is not a doctor or medical professional. At 38, she’s had a variety of professions including stand-up comedian, actor and restaurant server.

Through all those years, how Attention Deficient Hyperactivity Disorder works is something she has been learning about since she was diagnosed herself at the age of 12. Explaining that information is something she has done on her YouTube channel since 2016.

“Our brains are a piece of equipment we work with every day for everything that we do, so it’s critical to understand it,” she said.

She didn’t make the connection between her challenges and her diagnosis but things changed when she was in her twenties and found herself unable to complete college.

She began researching A.D.H.D. but had trouble organizing all the information she learned. So she turned to YouTube, a platform with which she was already familiar, to retain the material. “Notebooks, no, I lose notebooks,” she said. “YouTube. I won’t lose YouTube.”

In the beginning she found information for her videos on Google searches, but realized that there was a lot of misinformation about A.D.H.D. on the internet. “After I made it public, I thought, ‘I’m a college dropout. I don’t have a degree in this. I should not be educating people,’” she said.

Rachelle LeDuc-Cairns, a registered nurse in Canada, offered to teach her how to analyze research studies for their validity. Then Patrick LaCount, a post doctoral fellow at the Center for Child Health, Behavior and Development at Seattle Children’s Research Institute, began to meet with her weekly to review and discuss research studies. Today, she calls upon experts to help her on each subject, though her videos are not reviewed by a professional on a weekly basis.

“She has done a fine job popularizing the scientific findings in A.D.H.D. and bringing more attention to the condition, destigmatizing it and even motivating others with the condition and their families to obtain further information about it,” said Russell Barkley, a clinical professor of psychiatry at the Virginia Commonwealth University Medical Center.

The average age of her subscribers is between 18 and 24; many of the videos focus on themes relevant to young adults. One of Ms. McCabe’s main intentions is to address the stigma of taking medication for this group and about giving it to children. “I think there are a lot of moms that are tired of being told that they are drugging their children and that they are doing something wrong by treating their child’s medical condition,” she said.

In her video What I Want to Say to My Mom, Who “Drugged” Me, Ms. McCabe discusses being prescribed Adderall. (When she began taking medication, her grade point average went up a full point.) Medicating children has been controversial — though “Many of the medications used to treat A.D.H.D. have a long track record of safety and are research proven to be effective,” said Dr. Damon Korb, a developmental behavioral pediatrician in Los Gatos, Calif., and author of “Raising an Organized Child.”

It’s adults who are often overlooked. There are twice as many research studies for child A.D.H.D. compared to adult A.D.H.D. on the National Library of Medicine website, according to Ari Tuckman, a psychologist in West Chester, Pa., and author of the book, “A.D.H.D. After Dark: Better Sex Life, Better Relationship.”

“It’s only recently that they started to research A.D.H.D. in adults,” Ms. McCabe said. “Before that it was thought of as a childhood issue. So who cares how an eight-year-old might be in a domestic relationship since they’re not there yet.”

To that end, in one of her most popular videos, she talks about relationships and how people with A.D.H.D. may experience situations like becoming bored with their partner. “Getting involved with the nearest available human of the desired gender because they’re there and you’re bored? I’m pretty sure this is how Tinder works.”

Ms. McCabe thinks a lot about communication and word choice. Most of her videos open with the greeting “Hello brains.”

“Mr. Rogers had a whole bible of rules for how he used language on his show,” she said. “According to my community, one of the most helpful things I’ve done has been to give people the language to describe their challenges and the strategies.”

“I never heard of rejection sensitivity before, but as I watched the video, I instantly knew what it was,” said Kerrie McLoughlin, 50, a subscriber in Kansas City, Mo. She was diagnosed last year with A.D.H.D. “I teared up at the recognition in myself and started taking notes,” she said.

“I’d spent my life feeling serious anxiety over the smallest things, overthinking words I’d said and feeling enormously upset when things didn’t go perfectly,” said Celeste Perez, 33, an entrepreneur in Los Angeles, Calif. Diagnosed at 29, Ms. Perez used the channel to help explain her “A.D.H.D. quirks” to her husband in a way that did not involve boring, text-heavy studies.

Like many creators, Ms. McCabe now uses Patreon, which helps her amass paying subscribers. With nearly 3,000 subscribers, Patreon says her gross revenue there is $14,551 a month.

But her first donation came from Scot Melville, an engineer in San Francisco, who gave at the top tier of $100 per month along with a note about how the channel changed his life. “I increased my salary by over $100k per year over the course of four years,” said Mr. Melville, 36. “I credit much of that increase to the skills Jessica has given me through her videos.”

Now instead of donating money, Mr. Melville donates his time as the technology consultant on Ms. McCabe’s team.