Can you take Claritin and Robitussin together?
For most adults, yes: loratadine (Claritin) plus plain or DM Robitussin has no expected interaction. The one trap is a Robitussin variant that already contains an antihistamine or a decongestant.
Why
Claritin is loratadine, a non-drowsy second-generation antihistamine that "works by blocking the action of histamine" (MedlinePlus). "Robitussin" is not one drug but a brand family. Plain Robitussin is guaifenesin, an expectorant that "works by thinning the mucus in the air passages to make it easier to cough up" (MedlinePlus). Robitussin DM adds dextromethorphan, a cough suppressant. None of these three actively interact with loratadine: an antihistamine, an expectorant, and a cough suppressant act on different targets, so a healthy adult can generally take Claritin alongside plain or DM Robitussin. The catch is the label. Robitussin sells multi-symptom "cough + cold," nighttime, and severe-congestion versions that may add a second antihistamine (such as chlorpheniramine or diphenhydramine) or a decongestant (phenylephrine). Those extra ingredients, not the guaifenesin or dextromethorphan, are where doubling up matters.
What to watch for
Read the Drug Facts panel before combining. If your Robitussin variant already lists an antihistamine (chlorpheniramine, diphenhydramine, doxylamine), you would be taking two antihistamines at once, which stacks sedation and anticholinergic effects (dry mouth, drowsiness, urinary retention) even though Claritin alone is non-drowsy. If it contains a decongestant (phenylephrine, pseudoephedrine), that can raise blood pressure and heart rate, which matters if you have hypertension. Separately, the dextromethorphan in DM versions carries its own caution: MedlinePlus says do not use it if you take, or stopped within two weeks, an MAO inhibitor (isocarboxazid, phenelzine, selegiline, tranylcypromine), and clinicians extend that serotonin-syndrome caution to some SSRIs/SNRIs and other serotonergic drugs. That warning is about the DM, not about Claritin. Guaifenesin and dextromethorphan also appear in many other cold products, so avoid taking two products with the same ingredient. When in doubt, ask a pharmacist.
This is general reference, not medical advice, and not a guarantee of safety. Interactions depend on your doses, health conditions, and other medicines. Always confirm with your pharmacist or doctor before combining products, and follow the dosing on each label.