People get high because psychoactive substances hijack a reward circuit in the brain that evolved to reinforce survival behaviors like eating, sex, and social bonding. This circuit, centered on a small region called the nucleus accumbens, floods with dopamine and natural opioid-like chemicals when activated, producing feelings of pleasure, euphoria, or altered perception. Every addictive substance, from alcohol to cannabis to cocaine, triggers this same core pathway, though each does it through a different doorway.
About 292 million people worldwide used drugs in 2022, roughly 5.6% of those aged 15 to 64. That number doesn’t include alcohol, caffeine, or nicotine. The drive to alter consciousness is one of the most widespread human behaviors, and it has deep roots in both brain chemistry and psychology.
The Brain’s Reward Circuit
The feeling of being high starts in a pathway that connects two brain regions: the ventral tegmental area (VTA), which produces dopamine, and the nucleus accumbens, which receives it. Under normal conditions, this circuit activates when you do something beneficial for survival. Eat a good meal, and dopamine flows. Connect with someone you care about, and the same thing happens. The circuit essentially tells your brain: “That was good. Remember how you got it and do it again.”
Drugs of abuse shortcut this system. Instead of requiring you to actually do something rewarding, they trigger dopamine release directly or amplify it far beyond what natural rewards produce. Cocaine, for example, blocks the recycling of dopamine so it keeps stimulating the same receptors over and over. Amphetamines force dopamine out of nerve cells even when no signal tells them to release it. The result is a surge of pleasure that natural experiences rarely match.
Alongside dopamine, the brain’s own opioid system plays a major role. Your body produces natural opioid molecules, including endorphins and enkephalins, that contribute to feelings of well-being and pain relief. Drugs like heroin and prescription painkillers bind to the same receptors these natural molecules use, but with far greater intensity. Alcohol also partially works through this opioid system, which is one reason it produces that warm, relaxed feeling.
Why Different Substances Feel Different
All psychoactive substances converge on the dopamine reward pathway, but they take different routes to get there and activate different secondary systems along the way. That’s why a caffeine buzz feels nothing like a cannabis high, even though both involve dopamine.
Stimulants like cocaine and methamphetamine primarily supercharge dopamine and norepinephrine, a chemical that regulates arousal, attention, and mood. The combination produces intense energy, confidence, and euphoria. Methamphetamine also disrupts serotonin, a chemical involved in mood regulation and impulse control, which contributes to the erratic behavior associated with heavy use.
Cannabis works through a completely separate receptor system. Your brain produces its own cannabis-like molecules called endocannabinoids, particularly one called anandamide (named from the Sanskrit word for “bliss”). THC, the main psychoactive compound in marijuana, mimics anandamide and binds to the same receptors. This increases dopamine release in the reward pathway while also affecting memory, time perception, appetite, and pain sensation through cannabinoid receptors spread throughout the brain.
Psychedelics like psilocybin and LSD work primarily through the serotonin system. They activate a specific type of serotonin receptor on neurons in the cortex, the brain’s outer layer responsible for perception and thought. This activation triggers a cascade of intracellular signaling that alters how sensory information is processed, producing visual distortions, synesthesia, and the sense of expanded consciousness that users describe. The “high” from psychedelics is less about pleasure and more about radically changed perception.
Depressants like alcohol, benzodiazepines, and barbiturates enhance the brain’s primary inhibitory signaling system, essentially turning down the volume on neural activity. This produces relaxation, reduced anxiety, and lowered inhibitions. At higher doses, sedation and impaired coordination follow.
You Can Get High Without Drugs
The same chemical systems that drugs exploit also activate during certain natural experiences. The “runner’s high,” long attributed to endorphins, appears to depend heavily on endocannabinoids. During sustained aerobic exercise, blood levels of anandamide rise significantly. Because anandamide crosses into the brain and binds to the same cannabinoid receptors that THC targets, it produces a similar (though milder) effect: reduced anxiety and a gentle euphoria.
Other natural triggers for reward-circuit activation include intense social bonding, meditation, extreme sports, musical performance, and orgasm. Each of these activities releases some combination of dopamine, endorphins, or endocannabinoids. The brain doesn’t distinguish between “natural” and “artificial” activation of these pathways, which is precisely why substances are so effective at producing pleasure.
Why Humans Seek Altered States
The question isn’t just mechanical but psychological. People don’t get high simply because the brain chemistry allows it. They seek it out for reasons that appear to run deep in human nature.
One prominent explanation is self-medication. Psychiatrist Edward Khantzian first described this hypothesis in 1985, proposing that people use substances to cope with emotional pain, anxiety, or depression. Under this framework, someone with undiagnosed anxiety might drink because alcohol quiets the constant worry. Someone with chronic emotional numbness might use stimulants to feel something. The substance “works” in the short term, which reinforces continued use even as long-term consequences mount.
A broader evolutionary perspective suggests that intoxication itself may have served social functions throughout human history. Alcohol, in particular, appears to have facilitated cooperation and bonding in early human groups. By reducing the cognitive control that normally makes people guarded and cautious, intoxication may have helped strangers trust each other, share resources, and form the larger social networks that complex societies require. Some anthropologists argue that the desire to brew beer, not bake bread, was what first motivated humans to transition from foraging to farming.
Curiosity and pleasure-seeking also play straightforward roles. The reward circuit exists to motivate behavior, and the intense activation that substances provide is, at least initially, deeply appealing. Social pressure, cultural norms, boredom, and the simple availability of substances all lower the barrier to trying them.
Why the High Fades With Repeated Use
One of the most important things to understand about getting high is that the brain fights back. When receptors are activated repeatedly or continuously by a substance, the brain responds by reducing either the number of available receptors or their sensitivity. This process is called downregulation, and it’s the biological basis of tolerance.
With opioids, for example, repeated use disrupts a normal cycle where receptors are activated, pulled inside the cell for maintenance, and then returned to the surface in working condition. Morphine in particular interferes with this recycling process, leaving deactivated receptors stuck on the cell surface. The result is that the same dose produces less effect, pushing people to take more to achieve the same high.
This isn’t limited to opioids. Cannabis users experience downregulation of cannabinoid receptors. Stimulant users see reduced dopamine receptor availability. Alcohol users develop tolerance through changes in their inhibitory signaling receptors. In every case, the brain is attempting to restore its baseline state, a process called homeostasis. The drug pushes the system in one direction, and the brain pushes back.
The cruel consequence is that as tolerance builds, the person needs more of the substance just to feel normal, let alone high. Meanwhile, the brain’s recalibrated baseline means that without the substance, they feel worse than they did before they ever started using it. This is the transition point where use shifts from seeking pleasure to avoiding withdrawal, and it’s driven entirely by the brain’s attempt to adapt to a chemical it was never designed to handle on a daily basis.
The Gap Between First Use and Dependence
Three distinct brain regions map onto the stages of this progression. The nucleus accumbens drives the initial high, the pleasurable rush that makes someone want to repeat the experience. Over time, a nearby region called the dorsal striatum takes over, encoding the behavior as a habit rather than a conscious choice. The substance shifts from something you enjoy to something you do automatically, the way you might reach for your phone without thinking.
Meanwhile, the extended amygdala, a region involved in stress and negative emotions, becomes increasingly active during withdrawal. And the prefrontal cortex, which normally provides impulse control and long-term planning, becomes less effective at overriding the drive to use. The result is a brain that has been reorganized around the substance: motivated by habit, punished by absence, and less capable of choosing to stop.
None of this happens after a single use. The timeline varies enormously depending on the substance, the dose, the frequency of use, and individual genetics. But the underlying process is the same for every substance that produces a high: the reward circuit that made the first experience pleasurable gradually reshapes itself in ways that make continued use feel necessary.