- Some medications for cold and flu can react with caffeine, causing side effects for some people, like jitters and high blood pressure.
- Caffeine usually leaves your system after a few hours, so space out coffee from your medications.
- Staying hydrated when you’re sick is important, so try water, broth and herbal tea.
When you have a cold or the flu, reaching for an over-the-counter medication to take with your usual morning coffee may feel like second nature. But pairing caffeine, found in coffee, energy drinks and supplements, with certain cold and flu medications can do more harm than good.
That’s because the same enzymes in the liver break down caffeine and cold and flu medications. “So, when taken together, caffeine can alter the metabolism of these medications and often intensify their side effects,” explains Heather Gosnell, M.D.
While caffeine isn’t off-limits for everyone using cold or flu products, experts say it’s essential to know which ingredients may interact and how those combinations could make you feel when you’re trying to get better. We asked experts about which cold and flu medications don’t pair well with caffeine, what symptoms to watch for and other tips to maintain energy until you recover.
1. Pseudoephedrine (Sudafed)
“Pseudoephedrine is a decongestant with stimulant properties that can raise heart rate, which has an additive effect on the heart when combined with caffeine,” explains Seth Poulson, Pharm.D.
“The effects can compound when combined with caffeine, raising the risk of jitteriness, trouble sleeping and even higher blood pressure,” says Gosnell. Side effects can be more pronounced in people who are more sensitive to stimulants or who have a history of heart conditions, adds Poulson.
Research also suggests that combining caffeine and pseudoephedrine may lead to high blood sugar (hyperglycemia) and increase body temperature.
2. Dextromethorphan (Robitussin DM, Delsym)
Poulson explains, “Dextromethorphan affects the cough center of the brain.” This means that it temporarily relieves a cough but does not address the underlying cause of the cough or accelerate recovery.
Dextromethorphan can cause dizziness or mild drowsiness. Taking dextromethorphan at the same time as caffeine, a known stimulant, can confuse your body, masking the medication’s effects and potentially leading to individuals taking more medicine than necessary, notes Poulson.
He adds that although combining dextromethorphan and caffeine is not usually considered dangerous, it can cause people to feel off-balance, overstimulated or nauseous.
3. Phenylephrine (found in Tylenol Cold, DayQuil)
“Phenylephrine is similar to pseudoephedrine, but is significantly milder in its effect,” notes Poulson. Still, it can exacerbate the stimulating effects of caffeine, he adds.
“When combined with caffeine, it [phenylephrine] can increase the likelihood of side effects like dizziness, nervousness and difficulty falling asleep,” says Gosnell.
Both caffeine and phenylephrine are stimulants that can raise blood pressure and heart rate, and one small study found that phenylephrine plus caffeine may heighten cardiovascular side effects for some individuals, leading to an increased risk of high blood pressure or palpitations.
4. Diphenhydramine (Benadryl)
Diphenhydramine is a sedating antihistamine used to alleviate allergy symptoms or aid in nighttime relief from colds and flu. Because it’s sedating, diphenhydramine counteracts caffeine’s stimulant effects on the central nervous system.
Kiran Campbell, RDN, explains that combining antihistamines with caffeine sends mixed signals to the body, which may cause you to feel jittery yet fatigued as they simultaneously stimulate and sedate you.
“When used with caffeine, it can mask the drowsiness it causes, which may lead people to underestimate their fatigue,” Gosnell shares. This may cause individuals to unintentionally overuse the medication or engage in activities, such as driving, with impaired alertness, she adds.
How Long Should You Wait Before Having Caffeine?
There is no official length of time to wait between taking cold and flu medications and consuming caffeine, explains Poulson. That said, he generally recommends people wait two to three hours between medications and caffeine to help minimize any overlapping stimulating effects.
Caffeine typically remains in your system for approximately five hours, on average. “Therefore, individuals with health concerns may want to refrain [from taking cold and flu medications] for longer, though the time frame can vary depending on the amount consumed and your body’s metabolism,” notes Campbell.
Caffeine Alternatives for Cold and Flu
Consider alternatives to caffeine to maintain energy and focus, especially when using cold and flu medications. Still, remember that being sick takes a lot of energy from your body, and it is natural to feel fatigued.
- Supplement with creatine. “Supplemental creatine may help improve memory and cognitive function after a poor night of sleep,” says Ann Kent, M.S., RD, CDCES. Poor sleep often accompanies a cold or the flu, leaving you feeling fatigued and sluggish the next day.
- Switch to matcha or green tea. Caffeine from matcha or green tea offers a more gradual energy boost, comments Kent. It also has less caffeine than coffee, so drinking it instead when you have a cold or the flu may lessen some of the stimulating effects of the medication.
- Stay hydrated. “Dehydration worsens fatigue,” explains Campbell. Caffeine acts as a mild diuretic, adding to dehydration. Campbell recommends drinking warm liquids, such as herbal tea, broth or warm lemon water, to help soothe sore throats and loosen congestion, while promoting more natural energy levels.
- Eat balanced mini meals. Eating balanced mini meals at regular intervals provides your body with sustainable energy, especially if your appetite is low. Campbell suggests prioritizing nutrient-dense meals and snacks whenever possible.
- Try other pain relievers. Try taking noncaffeinated pain relievers, such as acetaminophen or ibuprofen, to stay alert without relying on caffeine, says Gosnell. Talk to your health care provider with any questions about medication or your symptoms.
Our Expert Take
Caffeine can interact with several common cold and flu medications, intensifying their side effects. If you’re sick and rely on caffeine for energy, check your medication’s active ingredients and consider alternative energy sources. “When you’re feeling well, caffeine can give you a quick energy boost, but when you’re sick, the best energy booster is rest, hydration and nourishment,” comments Campbell.
