How Much Caffeine You Should Actually Have—and When
Figure out the right amount of caffeine to boost alertness without disrupting your sleep
3 min
Caffeine can give us a boost, but too much can mess with our sleep and make us feel jittery. So how do we know what’s the right amount?
Generally, government and health groups recommend that healthy adults consume no more than 400 milligrams of caffeine a day. That comes out to about four, 8-ounce cups of coffee, says Jennifer Temple, a professor of exercise and nutrition sciences at University at Buffalo School of Public Health and Health Professions.
(No, that 20-ounce Starbucks Venti doesn’t count as one cup of coffee.)
And believe it or not, we are doing pretty well on this target. The average American adult consumes about 200 milligrams of caffeine a day and in Europe, it is 270 milligrams, according to a 2017 review study.
But not everyone is optimising their caffeine intake to maximise how it can help them—by sharpening concentration for work or giving them a boost before a run—without hurting their sleep or overall health.
Here’s how to think strategically about getting the most out of your daily dose.
Optimising the boost
Caffeine can help you focus and keep you alert.
About 100 to 150 milligrams—or one to 1.5 cups of coffee—is a ballpark amount that will deliver a boost, says Astrid Nehlig, an emeritus research director at the French National Institute of Health and Medical Research, who has studied caffeine’s impact on brain activity, though it varies from person to person.
The effects generally kick in about five minutes after consumption and increase to become optimal for between roughly 15 and 120 minutes, Nehlig says.
Caffeine has been linked to physical benefits, too. People walked more on days they drank coffee than on days they didn’t, according to a 2023 study of 100 people in the New England Journal of Medicine. Participants took an average of 1,000 more steps on days when they drank caffeinated coffee than when they didn’t.
Other studies have suggested that caffeine can sometimes help us work out harder, such as when we have it before high-endurance exercise like long runs or swims, or sports that require a sustained effort, like soccer, Nehlig says.
The same boost hasn’t been found with shorter efforts, such as a sprint. Caffeine doesn’t act directly on muscles but rather reduces your rate of perceived exertion and the time it takes you to feel exhausted.
The downsides
Caffeine’s main negative for your health is that it can disrupt your sleep.
The NEJM study that found that people walk more on days when they drink caffeine also found a downside. On days when study participants could drink as much caffeinated coffee as they wanted, they slept on average 30 minutes less than on days they didn’t drink any.
The impact on sleep varies greatly depending on how fast you metabolise caffeine, says Gregory Marcus, a cardiologist and professor of medicine at University of California, San Francisco and first author of the NEJM study.
On average, it takes about 4.5 hours for half of the caffeine consumed to pass through your system. However, genetic differences make some people metabolise it slowly or quickly, doctors and researchers say. The population is roughly split between fast and slow metabolisers.
The sleeping and walking study tested whether participants were slow or fast metabolisers of coffee. Those that were slow metabolisers slept nearly an hour less on the nights they drank caffeinated coffee, while the fast metabolisers didn’t experience any impact on sleep.
Where to get your caffeine
The best source of caffeine is unsweetened coffee or tea, says Dr. Frank Hu, professor of nutrition and epidemiology at Harvard T.H. Chan School of Public Health. These drinks have other beneficial ingredients, such as polyphenols, which have antioxidant effects which reduce inflammation.
The caffeine content in coffee and tea can vary, but soda can’t have more than 71 milligrams per 12 ounces, per Food and Drug Administration regulations.
Adults get most of their caffeine from coffee, but the market for energy drinks is growing. Pay extra attention to the caffeine in these drinks, because some contain very high levels.
Getting caffeine from soda or energy or sports drinks makes it more likely you are also getting a high dose of sugar and empty calories, says Hu.
Extra caution
Kids under 12 should avoid caffeine, while 12- to 18-year-olds should have no more than 100 milligrams a day, according to the American Academy of Pediatrics. Pregnant women are advised to have no more than 200 milligrams of caffeine a day.
People with chronic conditions like high blood pressure, diabetes or heart disease might want to be more cautious about their caffeine consumption, Hu adds. The NEJM study found that on the days when participants consumed caffeine, they had more abnormal heart rhythms in the lower chamber of the heart, which is associated with a greater risk of developing heart failure.
And people who get migraine headaches should try to drink no more than 100 milligrams of caffeine a day, the equivalent of a mug of coffee, says Dr. Amaal Starling, a headache specialist and neurologist at Mayo Clinic in Scottsdale, Ariz. She advises her patients who have daily or severe headaches not to drink any caffeinated beverages or switch to decaffeinated coffee.
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From making unpopular decisions to learning when to listen, leaders from five businesses reveal what nobody prepared them for — and how running a company has challenged their expectations.
Technology and semiconductor shares fell sharply as investors questioned the debt financing the AI infrastructure boom and confronted higher rates and Chinese competition.
Elon Musk is exploring a potential merger between Tesla and SpaceX, a deal that could reshape the future of AI, robotics, autonomous vehicles and space technology. With a combined valuation potentially reaching $3.5 trillion, the move could bring Musk’s vision of an interconnected technology ecosystem closer to reality, although a deal remains uncertain.
5 min
Elon Musk has engineered ties between Tesla TSLA 3.41%increase; up pointing triangle and SpaceX SPCX 7.79%increase; up pointing triangle that are hard to break, and now he wants to fuse them together permanently.
Musk has run both Tesla and SpaceX concurrently over the past two decades, using a schedule that dictated which days he spent focused on each business.
The companies have often shared resources and personnel, signaling their close ties. Last year, SpaceX looked into creating a spacesuit for Tesla’s humanoid robot Optimus, a person familiar with the matter said. Tesla last week showed off its new Roadster, a vehicle featuring SpaceX rocket thrusters that it hopes to soon bring to market.
And in recent months, Musk has repositioned both companies by expanding beyond their core operations toward a shared mission centered on artificial intelligence.
The world’s richest man on Tuesday signaled his interest in tying up SpaceX and Tesla, marking what would be the biggest corporate merger of all time. Because he serves as chief executive of SpaceX and Tesla, Musk said committees of independent directors at both companies are evaluating a possible deal, adding that a transaction might not come to fruition.
The committees will likely evaluate, with lawyers and bankers, how each company would fare in a potential deal and how a deal might best be structured. They then present their conclusions to their respective boards, who typically vote on whether to proceed.
“It’s an odd Kabuki dance where two groups of people are talking and I can’t be in the conversation,” Musk told SpaceX investors on Tuesday in response to an analyst’s question about a potential deal.
For Musk, the merger supports his vision of a world full of autonomous cars, humanoid robots and weekly rocket launches, as well as the data centers and satellites required to keep the whole thing running.
Some investors and analysts said they expect a transaction would be structured as an all-stock deal, with SpaceX potentially paying a modest premium for Tesla shares.
SpaceX, which has a market value of about $2 trillion, said it is seeing sharp growth in revenue across its businesses, which include operating data centers, launching rockets and operating satellite networks such as the internet service Starlink. Tesla is valued at about $1.5 trillion and is expanding its operations beyond its automotive and energy business. Shares in both companies traded higher following the news Tuesday.
Musk’s substantial ownership stakes in both companies, along with voting control at SpaceX, has enabled him to set the deal in motion. Analysts and investors said the deal will probably face regulatory scrutiny internationally, though some see Musk’s close relationship with the Trump administration as an asset to getting approval.
Blurred lines
The companies haven’t said which directors are on the special committees evaluating a potential deal. Several SpaceX and Tesla board members have either personal or business ties to Musk. And like Musk, venture capitalist Ira Ehrenpreis sits on both boards.
In a filing this week, Tesla outlined millions of dollars in business agreements with SpaceX and its subsidiaries last year, including $143 million in car sales to SpaceX, $3.3 million in advertising that it bought on the social-media platform X and $430 million in revenue from the sale of Megapack batteries for SpaceX’s data centers.
The companies also split the cost of resources including the use of Musk’s SpaceX jet and the bill for his personal security, which he runs through a private company.
Employees at both companies routinely move between companies to work on special projects, and some executives have dual roles, including Charles Kuehmann, vice president of materials engineering at both SpaceX and Tesla, and Ashok Elluswamy, the vice president of AI software at Tesla who runs a joint venture with SpaceX called Digital Optimus.
Over the years, Musk has launched new startups within his empire, including brain-implant company Neuralink, underground-tunnel developer the Boring Company and xAI, the AI startup that merged with SpaceX in February.
It is that AI business that Musk thinks can serve a market worth tens of trillions of dollars, justifying the need for a merger.
The business case goes like this: Tesla is developing robotaxis and robots, which it calls “physical AI.” SpaceX is working on the back end of physical AI: the data-center capacity and internet connection required for those robotaxis and robots to operate continuously.
“I don’t see what the value of Tesla is if it’s not merged with SpaceX,” said investment adviser Ross Gerber, a former Tesla bull turned critic invested in both companies. “If they don’t merge, the brains of everything that runs Tesla is owned by another company.”
On top of it all, both companies face constraints on the supply chains they need to make this world a reality, particularly when it comes to chips. To address this, Musk earlier this year announced a joint venture between Tesla, SpaceX and Intel to design and manufacture chips in Texas. “The most epic chip-building exercise by far,” he has said.
Musk at the wheel
For Musk, a merger would also solve two problems: demands on his attention and his lack of control at Tesla.
Tesla for years was Musk’s only public company, a status that came with greater scrutiny. There, Musk reports to a public board, as well as individual investors who make up around 30% of Tesla’s voting power, according to FactSet.
The question of Musk’s attention became a particular focus for investors and the board in recent years after he acquired Twitter in 2022 and launched xAI in 2023, and again in 2025 as he spent time in Washington, D.C., running the Department of Government Efficiency in the early months of President Trump’s second term.
As Tesla’s car business suffered in 2025, Musk threatened to take his AI ambitions outside the company if he wasn’t granted 25% voting control. Last November, Tesla shareholders approved a new pay package for Musk, which created a path for him to vastly expand his stake.
As of Sept. 30, Musk owned a roughly 20% stake in Tesla, according to the company’s proxy filing.
The SpaceX IPO gave Musk a different path. When SpaceX went public in June, the deal’s structure enabled him to have more than 80% voting power at the company—so much that he can’t be fired and decisions can’t be made without his support.
If SpaceX acquires Tesla, he will likely stay in control.
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