Is Benadryl Safe With 'Robitussin Cough And Cold 8-Hour'?

In our latest question and answer, the pharmacist discusses the use of Benadryl with 'Robitussin Cough and Cold 8-Hour'.


Can children's Robitussin Cough and Cold 8-hour (it contains chlorpheniramine and dextromethorphan) be taken with Benadryl if I alternate as needed?

Asked by Linda On Oct 14, 2022

Answered by
Medical Content Reviewed By HelloPharmacist Staff

Published Oct 14, 2022
Last updated Oct 14, 2022

Key points

  • Robitussin Cough And Cold 8-Hour should not be given at the same time as Benadryl as both contain antihistamines. Doing so would be considered a therapeutic duplication, increasing the risk of side effects.
  • 'Robitussin Cough And Cold 8-Hour' and Benadryl can be alternated by an appropriate amount of time and given during the same day.


Robitussin Cold & Cold Long-Acting 8-Hour (dextromethorphan; chlorpheniramine) should not be taken at the same time as Benadryl (diphenhydramine) as both contain an antihistamine. Combing them at the same time could increase the risk of side effects.

However, as mentioned in your question, these drugs could certainly be alternated and given during the same day (just not at the same time).

What Is In Robitussin Cold & Cold Long-Acting 8-Hour

Robitussin Cold & Cold Long-Acting 8-Hour contains the following two drugs:

  • Dextromethorphan (cough suppressant)
  • Chlorpheniramine (antihistamine)

It is the chlorpheniramine in this product we are concerned about giving with Benadryl.

Chlorpheniramine is a first-generation antihistamine contained in several over-the-counter products, including this one and most Dimetapp products.

Like Benadryl, it is sedating, but not quite to the degree that Benadryl is. It is more sedating than second-generation antihistamines (e.g., Claritin, Allegra) however.

One area where chlorpheniramine differs from Benadryl is its duration of action. While Benadryl lasts four to six hours per dose, chlorpheniramine lasts eight to twelve.

What Is Benadryl?

Benadryl contains to sedating antihistamine diphenhydramine. It is a first-generation antihistamine, can be used for allergy symptoms, and is very commonly used in over-the-counter sleep aids.

Concerns Combining Benadryl And Chlorpheniramine

Both Benadryl (diphenhydramine) and chlorpheniramine (contained in Robitussin Cold & Cold Long-Acting 8-Hour) can increase the risk of side effects. Combining both drugs would be considered a 'therapeutic duplication' as they are in the same drug class, work in the same manner, and have similar side effects. Side effects include:

  • Dizziness
  • Dry mouth
  • Sedation
  • Dry eyes
  • Constipation
  • Paradoxical excitation (in children)

Ideally, you want to separate the administration of these drugs. If you take Robitussin Cold & Cold Long-Acting 8-Hour first, you'll want to wait at least 8 to 12 hours before taking Benadryl. 

Similarly, if you take Benadryl first, you'll want to wait 4 to 6 hours before taking Robitussin Cold & Cold Long-Acting 8-Hour.

Final Words

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About the Pharmacist

Dr. Brian Staiger, PharmD

Dr. Brian has been practicing pharmacy for over 13 years and has wide-ranging experiences in many different areas of the profession. From retail, clinical, program development, and administrative responsibilities, he's your knowledgeable and go-to source for all your pharmacy and medication-related questions! Dr. Brian Staiger also has herbalist training and educational certificates in the field of medical ethnobotany. Feel free to send him an email at! You can also connect with Dr. Brian Staiger on LinkedIn.

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