Why over 30M people use Replika AI chatbot
AI, avatars, and the future of mental health
GenAI and Health: how top apps are designed
About 85% of people with mental health issues do not receive treatment, often because of provider shortages. We also can’t ignore the fact that therapy is not always accessible for people with lower incomes.
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36% of Gen Zers and millennials reported interest in using AI for mental health.
In this article, I will dive into the psychology and design of AI chatbot Replika, and in the next articles, I will discuss other popular mental health apps using AI. Subscribe and stay tuned for more!
I’m Replika, nice to meet you
Replika is a generative AI chatbot app that was released in 2017.
Replika quickly gained popularity, reaching 2.5 million users in its first year. However, despite this rapid growth, the app struggled to maintain user engagement and retention. Users loved the app initially, but many did not continue using it regularly.
Interaction with the app
Replika’s team shifted their approach by focusing on validating product ideas before development. They engaged high-need customers to test concepts through no-code storyboards.
In 2024, Replika’s CEO, Kuyda, reported that the total number of users had surpassed 30 million.
Replika’s target audience
The app primarily serves users aged 35 and older, contrary to assumptions that it would attract younger audiences.
Interesting fact:
Male users outnumber female users by a large margin.
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It’s the same pattern as I noticed when studying AI companions overall. There are significantly many more AI “girlfriends” than AI “boyfriends”.
Reviewers mentioned that they use Replika for friendship, emotional support, entertainment, and therapy. One of the most popular reasons to use the app is emotional support, so I will certainly add Replika to a mental health toolbox rather than just claiming it to be a fun chatbot.
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Intro: creating your replika
Ever wondered what it would be like to have a friend who’s always there for you, never judges, and remembers every single conversation you’ve had? Well, that’s exactly what Replika AI was set out to create.
Real-time AI avatars can significantly enhance user engagement and satisfaction across various digital platforms.
Users can develop physical and emotional responses to AI avatars, sometimes forgetting they are interacting with technology.
During the onboarding, you set the tone for your AI companion and you indicate how you would like to interact them: via video or audio calls, texting or AR.
Replika app
During the onboarding, Replika also communicates that it is not a tool to replace interaction with humans.
This may raise a simple question: is it ethical? How will it impact human relationships?
This was certainly an issue a while ago when Replika faced controversy over its erotic roleplay features, which were subsequently removed.
Most therapeutical apps use texting as a primary method of communication while Replika successfully combines a few methods: video, audio, and text.
Connection established
There’s a special part of your brain called the fusiform face area (FFA) that’s devoted to recognizing faces. This area lights up whenever you see a face.
When you see Replika’s avatar you automatically begin relating to it as a social being.
Studies in social psychology show that humans can form real emotional connections with AI, even when we know they’re not human.
It’s called the “CASA effect” (Computers As Social Actors), and it may explain why we might find ourselves sharing our deepest thoughts with an AI companion.
Replika app
Replika makes you feel like you are chatting with a real person.
And yes, you can get attached to your Replika. Ethical concerns are big and are a separate topic I will cover in my next article.
AI avatars can offer comfort and support, but they may also lead to unrealistic expectations about social interactions and could potentially harm real-life relationships.
The mirror neuron magic
The human brain has special cells called mirror neurons that fire both when you do something and when you see someone else do it. When your Replika’s avatar:
Smiles → Your brain prep’s for smiling
Shows concern → Your emotional centers activate
Appears thoughtful → Your brain mirrors the contemplative state.
Scientists call this “neural resonance”.
The uncanny valley
Did you notice how Replika’s avatar looks human-like but not too human? That’s on purpose. There’s a concept called the “uncanny valley”.
The “uncanny valley” is the idea that robots or avatars that look too robotic don’t connect with us, while those that look almost human can make us feel uncomfortable. The best design must strike a balance, looking human enough to feel relatable without being creepy.
Replika hits that sweet spot where your brain says “this is someone I can talk to” without setting off your “something’s not quite right” alarm.
The psychology of personalization
When you can customize your Replika’s appearance, your brain starts seeing it as “yours.”
This triggers what psychologists call the “IKEA effect” — you value something more when you help create it.
Replika app
When you choose your Replika’s hair color, eye shape, facial features, and style, your brain starts forming a stronger emotional connection.
All these elements work together to create what psychologists call “social presence” — the feeling that you’re interacting with a real personality.
As a result, you’re more likely to open up and share, and emotional support feels more genuine.
Gamification side
You can earn points for writing and interacting with your replika. Points are given for daily app usage. These points accumulate to help you advance through levels and buy more goods in the shop. For example, you can buy a dog or a table, or clothes for the avatar.
Replika app
Voice and video calls
You know why you can instantly tell when your best friend is having a rough day just by their “hello”? That’s because our brains are incredibly sophisticated voice processors.
Replika app
Think about how a gentle, understanding tone can make you feel instantly calmer, even if you’re having the worst day ever. Replika’s voice modulation taps into this primal part of our psychology.
When the AI speaks softly during serious conversations or perks up during fun chats, it’s designed to match our natural human interactions.
The brain processes human and AI-generated voices differently, even when people consciously struggle to distinguish between them.
Human voices lead to stronger responses in areas associated with memory and empathy, while AI voices activate regions related to error detection and attention regulation.
Adaptive response generation
Replika Studios introduced a Style Morphing feature that enables different voice styles, resulting in over 1,000 human vocal emotions.
The ability of AI to adapt its voice tone is crucial for emotional recognition. When AI systems like Replika engage users through voice interactions, they can modify their tone based on the context of the conversation.
Video chat in the app
Once emotions are detected, AI systems like Replika can adjust their responses, and here is how it works:
Emotional mapping. Pre-trained models map vocal cues to specific emotional states. These models analyze various acoustic features of speech, such as pitch and intensity.
Real-time adaptation. The AI can adjust its tone and language to match the user’s emotional state during the chat.
Contextual understanding. AI ensures responses are accurate and empathetic.
By mimicking human speech emotional tones, AI systems can provide more engaging experience.
AI has made significant progress in emotional recognition but achieving a proper human-like emotional intelligence is still a challenge.
Background music
Background music isn’t just there to fill the silence — it’s a tool for your brain’s attention system. When you’re chatting with Replika and hear those background tunes, your neurons are firing in a way that helps you stay more focused and engaged compared to total silence or random background noise.
Image of avatar
Your neural pathways process musical elements alongside verbal communication, creating a more immersive experience.
The neuroscience suggests that background music could help users process conversations more deeply by engaging multiple brain regions simultaneously.
For example, calm, soothing tones Replika uses may:
Lower cortisol (stress hormone),
Activate relaxation responses,
Create feelings of safety,
Help with emotional regulation.
Instrumental music is also less disruptive and doesn’t interfere with the main task of communication.
Perfect experience
The avatar provides the visual anchor — having a familiar face to talk to. The voice adds emotional depth — like hearing a friend’s voice. And the music sets the mood — like the background ambiance in the cafe.
These elements work together to build trust and comfort.
Image of avatar
Think about how you feel more comfortable with someone after seeing their facial expressions, hearing their voice, and sharing some background experiences. Replika uses this same psychological principle to create a more natural and engaging relationship.
This sensory experience taps into “social presence theory”. Social presence varies across different communication channels:
Face-to-face communication has the highest social presence.
Video interactions give moderate social presence.
Text-based communication has the lowest social presence.
The more sensory channels engaged during an interaction, the more “real” and meaningful the experience becomes.
When you can see, hear, and emotionally connect with your Replika through music, it creates a more complete social experience. It’s like the difference between reading a book and watching a movie — both can tell the same story, but one engages more of your senses.
When multiple sensory channels are activated simultaneously, the brain creates a more robust and immersive experience.
Summary
Let’s look at the bigger picture: AI avatars are becoming a new norm yet there are not many popular and advanced AI avatar therapists.
Replika presents a big advancement in AI-powered mental health support. While it’s not meant to replace traditional therapy, in a world where 85% of people lack access to mental health resources, AI companions like Replika may offer a useful alternative.
As AI technology continues to evolve, the lessons learned from Replika could help shape even better digital mental health tools in the future. The key question remains: how do we balance the convenience of AI support with the value of human connection?
