What affects your dreams: food, alcohol, medications, fever and more

Two routes: your sleep and your story

Things that affect your dreams usually work through one of two routes. The first changes how you sleep: how much REM sleep you get (the stage when dreams are most vivid) and how often you wake up during the night. The second slips into the plot itself: a sound, the heat or a body sensation that the dream turns into an image.

One detail is worth keeping in mind. Often you aren't dreaming more, you're remembering more. A dream mostly sticks when you wake up in the middle of it or right afterward. In a review of drugs and dreaming, Alain Nicolas and Perrine Ruby (2020) concluded that the best explanation for changes in dream recall is how often sleep gets interrupted, more than any change in REM sleep. That's why anything that breaks up your night can make it feel like you're dreaming more. We cover that side of things in our guide to remembering your dreams.

Food and late-night eating

The idea that food causes strange dreams goes way back. In 1904, the American cartoonist Winsor McCay launched a comic strip, Dream of the Rarebit Fiend, in which each character has a wild dream after a late supper of Welsh rarebit, a cheese-on-toast dish. A century later, Tore Nielsen and Russell Powell (2015) surveyed 396 Canadian students and found that about 18% believed food affected their dreams. Dairy was blamed most often, sweets came up for bizarre dreams, and spicy food for disturbing ones.

The researchers couldn't tell whether food was actually the cause. They offered several explanations that can overlap: heavy digestion or an intolerance, such as to lactose, might interrupt sleep; folklore might make people notice it more; or we might blame dinner for something that comes from elsewhere. What did stand out is that people who blamed food also slept worse. A big, late meal can wake you more often, and every awakening is another chance to remember a dream.

Caffeine and your dreams

No studies show that caffeine changes what you dream about. Its effect on dreams is indirect: taken late, it makes sleep shorter and lighter, with more awakenings, which can mean choppier dreams or remembering more fragments. In Nielsen and Powell's study, the people who thought food affected their dreams also drank more coffee, one more hint that broken sleep matters more than the menu.

How early to cut it off and where it hides are covered in our sleep hygiene guide. For your dream journal, it's enough to note when you had your last cup.

Alcohol: out like a light, then intense dreams

Alcohol changes dreams by changing the rhythm of the night. A review of sleep-lab studies (Ebrahim and colleagues, 2013) found that alcohol helps you fall asleep sooner and deepens the early part of the night, but it delays the first REM period at every dose and, at high doses, cuts REM in the first half. The second half of the night, by contrast, gets more restless, with more awakenings.

That combination explains a very common experience: after drinking, the early morning hours bring intense, sometimes distressing dreams that you half wake from and remember vividly. If you notice that nights out end in bad dreams, your journal will probably back you up.

Quitting cannabis or nicotine

Quitting cannabis after regular use often brings very vivid, strange dreams. A review by Alan Budney and colleagues (2004) in the American Journal of Psychiatry listed strange dreams among the symptoms of cannabis withdrawal, and the DSM-5 diagnostic manual gives disturbing dreams as an example of the sleep difficulty of that stage. According to Morten Hesse and Birgitte Thylstrup (2013), these dreams peak later than other symptoms, often after the first week, and last longer.

Something similar can happen with nicotine. The directions on 24-hour nicotine patches say that if you have vivid dreams or other sleep problems, you can take the patch off at bedtime and put on a new one in the morning. If quitting something is giving you rough nights, talk to your doctor or pharmacist: there are ways to make the process easier.

Medications that can change your dreams

Several common medications can change how you dream or how much you remember. If you take one and notice a change, don't stop it or change the dose on your own: ask your doctor first. Here are some examples with solid backing:

• Antidepressants. A systematic review by Tribl, Wetter and Schredl (2013) found that most of them reduce how often people recall dreams, though some can make dreams more intense. When people stop them, especially abruptly, the UK's Royal College of Psychiatrists lists vivid or frightening dreams among the withdrawal symptoms.
• Beta blockers. The NHS lists nightmares among the main side effects of propranolol and notes that they're usually mild and don't last long.
• Melatonin. Many people report more vivid dreams on it. There's no conclusive proof that melatonin is the cause; one possible explanation is that it may increase time spent in REM sleep.
• Varenicline, a medication to help you quit smoking. Its prescribing information warns that it can cause vivid, unusual or strange dreams.

Fever dreams

Fever dreams have a reputation for being weird, and research backs that up. Michael Schredl and Daniel Erlacher (2020) collected a hundred fever dream reports online and compared them with ordinary dreams from people of similar age and gender. The fever dreams were more bizarre, more negative in tone and more often about health and temperature: oppressive heat, rooms that warp, impossible tasks.

The authors suggest that fever, by temporarily throwing off how the brain works, may explain part of that strangeness. These dreams usually fade as the illness passes. If a fever is high or won't come down, that's a job for your doctor, not your journal.

Your sleep position

The position you sleep in might nudge your dreams a little, though the evidence is weak. In Hong Kong, Calvin Kai-Ching Yu (2012) asked 670 people, mostly students, about their usual sleep position and their dreams. Stomach sleepers reported more dreams about sex, being locked up, being unable to breathe or being naked. Yu suggested that pressure on the chest and harder breathing might seep into the dream, but that's a hypothesis.

A smaller Turkish study (Agargun and colleagues, 2004) of 63 people found more nightmares among left-side sleepers than right-side sleepers. These are correlations in small groups, not proven causes. There's no need to change how you sleep because of them; if you're curious, note your position in your journal and see what you find.

Temperature, sounds and smells

Your bedroom reaches your dreams in two ways. Temperature changes your sleep: a review by Kazue Okamoto-Mizuno and Koh Mizuno (2012) concluded that heat, with bedding and clothing, increases wakefulness and reduces deep and REM sleep. A hot night often means more awakenings and, with them, more remembered dreams.

Outside stimuli also slip into the story. In a classic experiment, William Dement and Edward Wolpert (1958) sprayed sleeping volunteers with cold water, and some went on to dream about rain or water. Ralph Berger (1963) spoke people's names during REM sleep, and an independent judge could often link elements of the dreams that followed to the name that had been heard. With smells, a team led by Michael Schredl (2009) found that odors changed the emotional tone more than the content: the scent of roses went with more pleasant dreams than the smell of rotten eggs. It's the same reason your phone alarm sometimes turns into a doorbell or a siren inside a dream.

Run your own experiment with your journal

The best way to find out what affects your dreams is to watch yourself. For two or three weeks, next to each dream, jot down a few details about the night before. Then read it back and look for patterns:

• When you ate dinner, what it was, and whether you went to bed on a full stomach.
• Your last caffeinated drink and, if you drank alcohol, how much and when.
• Any medications or supplements you took, without changing them on your own.
• Whether you were hot, cold or bothered by noise, and what position you woke up in.
• How many times you woke up during the night.
• Change one thing at a time, like eating dinner earlier, and remember that a pattern in your journal is a clue, not proof.