I had two mysteries that were hanging over me.

I didn't understand them

and, to be honest, I was quite afraid to look into them.

The first mystery was, I'm 40 years old,

and all throughout my lifetime, year after year,

serious depression and anxiety have risen,

in the United States, in Britain,

and across the Western world.

And I wanted to understand why.

Why is this happening to us?

Why is it that with each year that passes,

more and more of us are finding it harder to get through the day?

And I wanted to understand this because of a more personal mystery.

When I was a teenager,

I remember going to my doctor

and explaining that I had this feeling, like pain was leaking out of me.

I couldn't control it,

I didn't understand why it was happening,

I felt quite ashamed of it.

And my doctor told me a story

that I now realize was well-intentioned,

but quite oversimplified.

Not totally wrong.

My doctor said, "We know why people get like this.

Some people just naturally get a chemical imbalance in their heads --

you're clearly one of them.

All we need to do is give you some drugs,

it will get your chemical balance back to normal."

So I started taking a drug called Paxil or Seroxat,

it's the same thing with different names in different countries.

And I felt much better, I got a real boost.

But not very long afterwards,

this feeling of pain started to come back.

So I was given higher and higher doses

until, for 13 years, I was taking the maximum possible dose

that you're legally allowed to take.

And for a lot of those 13 years, and pretty much all the time by the end,

I was still in a lot of pain.

And I started asking myself, "What's going on here?

Because you're doing everything

you're told to do by the story that's dominating the culture --

why do you still feel like this?"

So to get to the bottom of these two mysteries,

for a book that I've written

I ended up going on a big journey all over the world,

I traveled over 40,000 miles.

I wanted to sit with the leading experts in the world

about what causes depression and anxiety

and crucially, what solves them,

and people who have come through depression and anxiety

and out the other side in all sorts of ways.

And I learned a huge amount

from the amazing people I got to know along the way.

But I think at the heart of what I learned is,

so far, we have scientific evidence

for nine different causes of depression and anxiety.

Two of them are indeed in our biology.

Your genes can make you more sensitive to these problems,

though they don't write your destiny.

And there are real brain changes that can happen when you become depressed

that can make it harder to get out.

But most of the factors that have been proven

to cause depression and anxiety

are not in our biology.

They are factors in the way we live.

And once you understand them,

it opens up a very different set of solutions

that should be offered to people

alongside the option of chemical antidepressants.

For example,

if you're lonely, you're more likely to become depressed.

If, when you go to work, you don't have any control over your job,

you've just got to do what you're told,

you're more likely to become depressed.

If you very rarely get out into the natural world,

you're more likely to become depressed.

And one thing unites a lot of the causes of depression and anxiety

that I learned about.

Not all of them, but a lot of them.

Everyone here knows

you've all got natural physical needs, right?

Obviously.

You need food, you need water,

you need shelter, you need clean air.

If I took those things away from you,

you'd all be in real trouble, real fast.

But at the same time,

every human being has natural psychological needs.

You need to feel you belong.

You need to feel your life has meaning and purpose.

You need to feel that people see you and value you.

You need to feel you've got a future that makes sense.

And this culture we built is good at lots of things.

And many things are better than in the past --

I'm glad to be alive today.

But we've been getting less and less good

at meeting these deep, underlying psychological needs.

And it's not the only thing that's going on,

but I think it's the key reason why this crisis keeps rising and rising.

And I found this really hard to absorb.

I really wrestled with the idea

of shifting from thinking of my depression as just a problem in my brain,

to one with many causes,

including many in the way we're living.

And it only really began to fall into place for me

when one day, I went to interview a South African psychiatrist

named Dr. Derek Summerfield.

He's a great guy.

And Dr. Summerfield happened to be in Cambodia in 2001,

when they first introduced chemical antidepressants

for people in that country.

And the local doctors, the Cambodians, had never heard of these drugs,

so they were like, what are they?

And he explained.

And they said to him,

"We don't need them, we've already got antidepressants."

And he was like, "What do you mean?"

He thought they were going to talk about some kind of herbal remedy,

like St. John's Wort, ginkgo biloba, something like that.

Instead, they told him a story.

There was a farmer in their community who worked in the rice fields.

And one day, he stood on a land mine

left over from the war with the United States,

and he got his leg blown off.

So they him an artificial leg,

and after a while, he went back to work in the rice fields.

But apparently, it's super painful to work under water

when you've got an artificial limb,

and I'm guessing it was pretty traumatic

to go back and work in the field where he got blown up.

The guy started to cry all day,

he refused to get out of bed,

he developed all the symptoms of classic depression.

The Cambodian doctor said,

"This is when we gave him an antidepressant."

And Dr. Summerfield said, "What was it?"

They explained that they went and sat with him.

They listened to him.

They realized that his pain made sense --

it was hard for him to see it in the throes of his depression,

but actually, it had perfectly understandable causes in his life.

One of the doctors, talking to the people in the community, figured,

"You know, if we bought this guy a cow,

he could become a dairy farmer,

he wouldn't be in this position that was screwing him up so much,

he wouldn't have to go and work in the rice fields."

So they bought him a cow.

Within a couple of weeks, his crying stopped,

within a month, his depression was gone.

They said to doctor Summerfield,

"So you see, doctor, that cow, that was an antidepressant,

that's what you mean, right?"

(Laughter)

(Applause)

If you'd been raised to think about depression the way I was,

and most of the people here were,

that sounds like a bad joke, right?

"I went to my doctor for an antidepressant,

she gave me a cow."

But what those Cambodian doctors knew intuitively,

based on this individual, unscientific anecdote,

is what the leading medical body in the world,

the World Health Organization,

has been trying to tell us for years,

based on the best scientific evidence.

If you're depressed,

if you're anxious,

you're not weak, you're not crazy,

you're not, in the main, a machine with broken parts.

You're a human being with unmet needs.

And it's just as important to think here about what those Cambodian doctors

and the World Health Organization are not saying.

They did not say to this farmer,

"Hey, buddy, you need to pull yourself together.

It's your job to figure out and fix this problem on your own."

On the contrary, what they said is,

"We're here as a group to pull together with you,

so together, we can figure out and fix this problem."

This is what every depressed person needs,

and it's what every depressed person deserves.

This is why one of the leading doctors at the United Nations,

in their official statement for World Health Day,

couple of years back in 2017,

said we need to talk less about chemical imbalances

and more about the imbalances in the way we live.

Drugs give real relief to some people --

they gave relief to me for a while --

but precisely because this problem goes deeper than their biology,

the solutions need to go much deeper, too.

But when I first learned that,

I remember thinking,

"OK, I could see all the scientific evidence,

I read a huge number of studies,

I interviewed a huge number of the experts who were explaining this,"

but I kept thinking, "How can we possibly do that?"

The things that are making us depressed

are in most cases more complex than what was going on

with this Cambodian farmer.

Where do we even begin with that insight?

But then, in the long journey for my book,

all over the world,

I kept meeting people who were doing exactly that,

from Sydney, to San Francisco,

to São Paulo.

I kept meeting people who were understanding

the deeper causes of depression and anxiety

and, as groups, fixing them.

Obviously, I can't tell you about all the amazing people

I got to know and wrote about,

or all of the nine causes of depression and anxiety that I learned about,

because they won't let me give a 10-hour TED Talk --

you can complain about that to them.

But I want to focus on two of the causes

and two of the solutions that emerge from them, if that's alright.

Here's the first.

We are the loneliest society in human history.

There was a recent study that asked Americans,

"Do you feel like you're no longer close to anyone?"

And 39 percent of people said that described them.

"No longer close to anyone."

In the international measurements of loneliness,

Britain and the rest of Europe are just behind the US,

in case anyone here is feeling smug.

(Laughter)

I spent a lot of time discussing this

with the leading expert in the world on loneliness,

an incredible man named professor John Cacioppo,

who was at Chicago,

and I thought a lot about one question his work poses to us.

Professor Cacioppo asked,

"Why do we exist?

Why are we here, why are we alive?"

One key reason

is that our ancestors on the savannas of Africa

were really good at one thing.

They weren't bigger than the animals they took down a lot of the time,

they weren't faster than the animals they took down a lot of the time,

but they were much better at banding together into groups

and cooperating.

This was our superpower as a species --