The World Health Organization estimates that more than 300 million people suffer from clinical depression world-wide. But cost, time, stigma, distance to travel, language barriers and other factors prevent many from seeking help.

Now, a growing group of health-care providers are betting that technology—from web-based courses to mobile apps that send prompts via text—can help bridge that gap.

It might seem surprising, since therapy, more than many other kinds of medicine, is so focused on the relationship between patient and therapist. But research, including a meta-analysis of studies involving internet-based cognitive behavioral therapy, or CBT, suggests that digital therapies augmented by coaches who are available by text or phone can be as effective as evidence-based traditional therapy in treating some people with depression.

One study, funded by the National Institutes of Health and involving 99 patients with moderate depression, found that 90 of them completed a full eight-week course that included access to a suite of treatment apps and text support from coaches with at least a bachelor’s degree in psychology. On average, those who completed the course experienced a significant decrease in symptoms of depression, with three-fourths meeting the criteria for full remission. On average, participants used the apps more than 195 times over two months and interacted with a coach about twice a week.

Elsewhere, a study by the U.K. National Health Service, based on 1.2 million referrals for depression and anxiety, showed that computerized CBT administered to people with depression yielded a recovery rate of 58.4%, compared with 53.9% for those undergoing several types of in-person therapy. Ricardo F. Muñoz, a professor and founder of the Institute for International Internet Interventions for Health at Palo Alto University, who wasn’t involved in the research, says that while patients with more severe depression may be more likely to seek in-person therapy, “the fact that much mild or clinical depression can be successfully treated with computerized CBT is of note.”

Clinical psychologists put the first digital interventions for depression online about 15 years ago, according to Stephen Schueller, an assistant professor of preventive medicine at Northwestern University and a member of Northwestern’s Center for Behavioral Intervention Technologies. “We basically thought, if it works in a self-help book, it will work online,” he says. But what they found was that it was difficult to motivate patients with depression to engage regularly with what were essentially online PowerPoint presentations.

Over the past five years, online therapies have evolved to include mobile apps such as Joyable, Lantern and Ginger.io, which are more personalized and responsive. They typically ask users to enter information about their moods and behaviors, then offer problem-solving suggestions, prompts to help patients retrain responses to negative situations, and daily health tips.

Dr. Schueller believes digital interventions need to continue evolving with technology to remain effective. “The future is trying to better understand how to make these apps and sites engaging,” he says. “That will include clinical psychologists working with experts in augmented reality, virtual reality and gaming to develop mobile solutions that are truly novel.”

One such tool might look like Koko, an online messaging chatbot that uses the internet community to address emotional distress. With Koko, a user puts in a negative thought, like ‘I’m stupid,’ and sends it out to other people who may be working through similar situations, Dr. Schueller says. “The crowd creates responses, which go through the system and come back to you as a new message: ‘Maybe you didn’t fail because you’re stupid, but maybe because you didn’t sleep enough or you didn’t study enough.’ ”

The idea is that the crowd “can provide many different ideas that, when combined, might produce better or more creative solutions” than a therapist can, says Dr. Schueller, adding that Koko also uses machine learning to identify those in need of more direct intervention or support.

Lynn Bufka, associate executive director of practice research and policy at the American Psychological Association, says research has demonstrated that individuals can benefit from a range of technology-enabled services. As such, she would like to see a more “stepped” approach to mental-health care for individual patients.

Stepped care might start with a brief in-person assessment of a patient who shows signs of depression, so that therapists can identify any behavioral or health concerns, says Dr. Bufka, who believes that a human should always be involved at the beginning of a treatment process. “Then, depending on severity, we would provide each patient with a self-help book or access to web-based education. If that didn’t work, perhaps we’d move to a computer-assisted intervention, and then move toward in-person treatment,” either group or individual sessions, Dr. Bufka says. The stepped-care system exists in the U.K., she says, where providers in the National Health Service identify patients with moderate depression and other problems and offer self-help or technology-enabled services. “I think we’ll ultimately see a combination of different online interventions” for depression, she says.

Dr. Muñoz of Palo Alto University says he also believes that therapeutic and preventive services for depression could fall on a continuum.

The challenge for the public is knowing which digital tools to trust, he says, pointing to PsyberGuide, a website headed by Dr. Schueller that uses a standardized rating system to help consumers select products and apps for various mental-health conditions, as a good model.

Eventually, Dr. Muñoz envisions something he calls massive open online interventions, where therapeutic and preventive services could be delivered virtually to anyone in the world, in any language, at any time—ideally at no charge to users. The only barrier to entry would be internet access. Once the technology is built and more people use it, he says, the marginal cost of providing that intervention to one more person would gradually approach zero.

He points to a study he conducted in which 15,170 smokers from around the world participated in a free online smoking-cessation program offered in English and Spanish. After 12 months, 3,479 users, or 23%, reported they had quit smoking; to help that many people quit using more common care, he says, health providers would have had to give nicotine patches to 17,395 smokers, at a cost of $3.65 million.

His program, which had been built with earlier research grants, cost a total of $200,000 to maintain and advertise the website world-wide for 30 months.

“With the political will and across-the-board standards, we can give an intervention to anyone, even people who don’t have access to a mental-health clinic or antidepressants,” he says. “All they need is access to a smartphone with a data plan.”

Ms. Mitchell is a writer in Chicago. Email her at reports@wsj.com.

Appeared in the June 26, 2017, print edition as ‘To Treat Depression, Start With a Digital Therapist.’