Social networks, for many, can prove to be an addictive technology, according to one of Facebook’s founders.

Sean Parker, a founding president of Facebook, offers a perspective on the growing power and effects of the social networks, which now have scale and reach unknown in human history.

The trend has led Parker to raise some red flags.

Parker adds that a widely used service like Facebook, which now has 2 billion monthly users around the world, “literally changes your relationship with society, with each other.”

Parker is now founder and chairman of the Parker Institute for Cancer Immunotherapy, and he spoke recently at an Axios event at the National Constitution Center in Philadelphia, about accelerating cancer innovation.

“When Facebook was getting going, I had these people who would come up to me and they would say, ‘I’m not on social media.’ And I would say, ‘OK. You know, you will be,’” he said. “And then they would say, ‘No, no, no. I value my real-life interactions. I value the moment. I value presence. I value intimacy.’ And I would say, … ‘We’ll get you eventually.'”

Looking back, Parker said he wasn’t sure he knew the consequences of what he was saying.

“That is because [of] the unintended consequences of a network when it grows to a billion or 2 billion people and … it literally changes your relationship with society, with each other … It probably interferes with productivity in weird ways,” he said. “God only knows what it’s doing to our children’s brains.”

The overriding goal of building the applications was to consumer as much of the user’s time and and conscious attention as possible, he added.

“And that means that we need to sort of give you a little dopamine hit every once in a while, because someone liked or commented on a photo or a post or whatever,” Parker added. “And that’s going to get you to contribute more content, and that’s going to get you … more likes and comments.”

As a result, it becomes a circle of social-validation.

“The inventors, creators — it’s me, it’s Mark [Zuckerberg], it’s Kevin Systrom on Instagram, it’s all of these people — understood this consciously,” he said, with a pause. “And we did it anyway.”

Parker isn’t the only tech executive to express dismay and worry over the monster that they helped create.

Tristan Harris, a former Google employee, has been outspoken in his criticism of how tech companies’ products hijack users’ minds.

“If you’re an app, how do you keep people hooked? Turn yourself into a slot machine,” he wrote in a widely shared Medium post in 2016. “We need our smartphones, notifications screens and web browsers to be exoskeletons for our minds and interpersonal relationships that put our values, not our impulses, first,” he continued. “People’s time is valuable. And we should protect it with the same rigor as privacy and other digital rights.”