Theraflu’s daytime formulas are designed to be non-drowsy, while its nighttime formulas deliberately cause drowsiness to help you sleep. The key difference comes down to one ingredient: the nighttime version contains an antihistamine (chlorpheniramine) that the daytime version leaves out.
What’s in Daytime vs. Nighttime Theraflu
Theraflu Daytime contains two active ingredients: acetaminophen (1,000 mg per dose) for pain and fever, and dextromethorphan (30 mg) to suppress coughing. Neither of these is classified as a sedating ingredient, which is why the daytime formula carries no drowsiness warning on its label.
Theraflu Nighttime shares those same two ingredients but adds chlorpheniramine maleate (4 mg), a first-generation antihistamine. This is the ingredient responsible for the “marked drowsiness may occur” warning printed on the nighttime box. First-generation antihistamines cross into the brain and block signals that keep you alert, which is why they’re so effective at making you sleepy. The nighttime label also warns that alcohol, sedatives, and tranquilizers can intensify that effect.
Daytime Theraflu Can Still Affect How You Feel
Calling the daytime formula “non-drowsy” is accurate in the sense that it lacks a sedating antihistamine, but that doesn’t mean it’s side-effect-free. Dextromethorphan lists drowsiness, dizziness, and lightheadedness among its possible side effects at normal doses. These effects are uncommon enough that the product doesn’t carry a drowsiness warning, but some people are more sensitive than others.
Some daytime Theraflu formulations also include phenylephrine, a nasal decongestant. Phenylephrine tends to push in the opposite direction: its reported side effects include nervousness, restlessness, anxiety, and insomnia. So rather than making you sleepy, the decongestant component may actually make it harder to relax or fall asleep if you take a dose too late in the day.
Driving and Daily Activities
The FDA warns that certain cold medicines, particularly those containing antihistamines or nighttime sleep aids, can make driving dangerous. Theraflu Nighttime falls squarely into that category. The daytime formula doesn’t carry the same driving restriction, but the FDA’s general advice is worth following: try any new over-the-counter medicine for the first time when you won’t need to drive, just to see how your body reacts. Dizziness or lightheadedness from dextromethorphan, even if uncommon, could still catch you off guard.
Dosing and Safety Basics
For the daytime caplet version, the recommended dose is two caplets every six hours while symptoms last, with a maximum of six caplets in 24 hours. It’s not approved for children under 12.
The most important safety concern applies to both daytime and nighttime formulas: acetaminophen and your liver. Each dose contains 1,000 mg of acetaminophen, which means hitting the daily maximum of six caplets puts you at 3,000 mg for the day. The label warns that severe liver damage can occur if you exceed 4,000 mg of acetaminophen in 24 hours. That threshold is easier to reach than you might think if you’re also taking other products that contain acetaminophen, like Tylenol, certain migraine medications, or other combination cold remedies. Check the active ingredients on everything you’re taking during cold and flu season to avoid accidentally doubling up.
Drinking three or more alcoholic beverages a day while using any acetaminophen product also raises liver risk significantly.
Picking the Right Formula
If you need to stay alert during the day, stick with Theraflu Daytime or any Theraflu product labeled “Daytime” or “Non-Drowsy.” If you’re dealing with symptoms at night and want help sleeping, the Nighttime version’s antihistamine serves double duty by easing runny nose and sneezing while also helping you doze off. Many people buy the combo pack and use each formula at the appropriate time of day.
One thing to watch for: Theraflu sells several product lines (Flu Relief, Severe Cold, ExpressMax), and the exact ingredient mix varies between them. Some daytime versions include phenylephrine for congestion, others don’t. Flip the box over and read the active ingredients panel rather than relying on the product name alone. The presence or absence of an antihistamine (chlorpheniramine or diphenhydramine) is the single clearest indicator of whether a formula will make you drowsy.