Can I take robitussin cf and benadryl (diphenhydramine)?

No interaction. Assuming you have symptoms for which guaifenesin, dextromethorphan, phenylephrine, and diphenhydramine (Benadryl) are indicated...there should be no interaction between these medications. Always read OTC medicine labels and ask the pharmacist whether your symptoms match the active ingredients! Sometimes less is more, so be careful with polypharmacy. Thank you for trusting HealthTap! Good luck--
No interaction . I don't see interaction between rob cold and flu and regular Benadryl (diphenhydramine) - but I would try one drug and see if it helps before adding a second one- also you can have local pharmacy check all your medications for interaction .