How to Reclaim Your Brain in 2026 - Dr Andrew Huberman (4K)

Most people think about cortisol as a bad thing that you want less of. Is that the right way to think about it?

Not at all. Cortisol has been labeled a stress hormone, and it is involved in stress. When you have a bout of stress, you get a spike of cortisol, so to speak. Um, cortisol, like other steroid hormones, is bound to things, and there's a f- a free form of cortisol, that's the active one. Um, you don't want your free unbound cortisol to be chronically high. But we need to really think about why it was called a stress hormone in the first place, and the main reason is cortisol's job is to deploy energy sources for your brain and body, to be able to react to things, think, and move. So cortisol naturally goes up a bit during stress, and it comes back again, provided you don't ruminate on that stress too much, on the stressor that is. The big eye-opener for me was when I actually went into the modern textbooks on cortisol. Not the ones that most medical students learn from, but what the endocrinologists, the specialists really learn from, and what the circadian and sleep biologists now understand, which is the reason you wake up every single morning, even if you have an alarm clock, is because of something called the cortisol awakening response. So if we just step back from a, a typical, healthy 24 hours, it looks something like this. Uh, a couple of hours before sleep, your cortisol is low. Your heart rate's low, you're calm, hopefully it's dim in the room, you go to sleep. Your cortisol is then at its absolute lowest levels for the entire 24 hours, and by the way, this is the same time when melatonin, the sleepy hormone, is at its highest levels. After about four, five hours of sleep, and typically in that first four, five hours of sleep is when you get your most deep sleep, slow wave sleep, non-REM sleep, many people experience a transition into the s- sort of last third of their sleep for the night, and they tend to wake up around that time, and often they use the restroom, go back to sleep. Why do they wake up? Well, it turns out that your cortisol is starting to rise about two thirds of the way through the night. I mean, it's really creeping up throughout the entire night, but it's gone from this nadir to it's starting to climb, and then at some point, let's assume you get back to sleep or you slept through the night, at some point, maybe 6:00 AM, maybe 8:00 AM, depends on who you are and what your schedule is, you wake up. Maybe your alarm clock goes off. You wake up. You wake up because the cortisol level reached a certain threshold. It is literally the cortisol awakening response. It is healthy, it is good, and you're, if I were to measure your cortisol at that moment, and compare it to what nor- people might call, like, a stress episode in the afternoon, you would say it's much higher than what stress induced. Okay, so then your cortisol continues to rise, and there's this unique opportunity in the first hour, maybe 90 minutes, but in the first hour after waking where viewing bright light can increase your morning cortisol spike, as I'll refer to it, by up to 50%. Bright light can come from sunlight, ideally, or from a bright artificial light like a 10,000 lux artificial light, or even a very bright indoor artificial LED or incandescent light. Okay, why is this important? Well, we could explore all the biology of cortisol and we can summarize it by saying you have this hypothalamic-pituitary-adrenal axis that sets off cortisol, self-regulates, negative feedback loop, et cetera, et cetera. That's the normal regulation of cortisol, which basically can be summarized as it never allows you to have your cortisol too high for too long. It feeds back on itself and shuts it down. However, in the first hour after waking, your brain's circadian clock has a unique privileged pathway that is separate from the HPA axis where it can amplify cortisol only in that first hour. So you say, "Why would that be?" This is nature's evolutionarily hardwired mechanism for giving you the opportunity to boost your cortisol so that you have energy to lean into the activities of your day. When I say energy, I'm not saying l- you know, it's not like w- happen to be in California at the moment, but not energy-energy. I'm talking about glucose mobilization. If you're on a low carbohydrate diet, you're gonna, you're gonna mobilize other energy sources. Your brain and body wakes up because of cortisol. You have the opportunity to boost that wakefulness even further by viewing bright light. Yes, you could exercise, yes, you could drink caffeine. Turns out caffeine, if you're a chronic caffeine user, such as me, such as you, doesn't actually increase cortisol that much. You could jump in a 40 degree Fahrenheit cold plunge, doesn't actually increase your cortisol. All this n- nonsense going around the internet about, oh, you know, women shouldn't do a cold plunge and if they do, not as cold, okay, maybe, but it's always attributed to increases in cortisol. Cold plunge reduces your cortisol levels. You can look at the data. The data show that it goes down. Adrenaline goes up, dopamine goes up, norepinephrine go up. So cortisol makes you alert, it makes you focus, and here's the key thing. Spiking your cortisol in that first hour after waking is so, so important, because that negative feedback loop mechanism kicks in about three hours after you've been awake, and that's why your cortisol then starts to drop late morning, early afternoon, later afternoon, and in the afternoon, if you have a bout of stress, no problem. You just have a little bit of cortisol bump, adrenaline bump, and it goes back down. If you don't spike your morning cortisol, what ends up happening is your cortisol system, essentially the HPA axis, is primed for stress events to give you big lasting increases in cortisol later which make it hard to fall asleep, which make it hard to stay asleep, which are part of the reason why people have afternoon anxiety-