CheratussinIt is not recommended to take Cheratussin and Benadryl together due to their additive effects on CNS (central nervous system) depression.

Cheratussin (Robitussin With Codeine)

Cheratussin AC is a prescription cough medication that contains two ingredients, codeine and guaifenesin. Guaifenesin is an expectorant, and helps to loosen up any congestion and mucus in your respiratory tract so that your body can remove it through coughing. Codeine is an opioid narcotic that suppresses the cough reflex in your brain, leading to cough suppression. It is important to note that codeine is a narcotic and not using Cheratussin AC as prescribed can lead to addiction, overdose, and in severe cases death.

Side effects of guaifenesin include drowsiness and dizziness. Common side effects of codeine include drowsiness, euphoria, rash, nausea/vomiting, and constipation. Serious side effects associated with codeine in cases of overdose include difficulty breathing, coma, hallucination and disorientation, and death.


Benadryl (diphenhydramine) is an antihistamine used to treat insomnia, itching, allergic reactions, and seasonal allergies. Histamine causes symptoms such as itchy eyes, sneezing, itchy skin, runny nose, and severe allergic reactions such as anaphylaxis. Diphenhydramine works by preventing histamine from binding to the histamine-1 receptor thereby preventing these symptoms from occurring. Common side effects of diphenhydramine include dry mouth, sleepiness, excitement, difficulty urinating, and blurry vision. Diphenhydramine is not recommended for use in patients >65 years old because these patients tend to experience more severe side effects than younger patients.

Taking Benadryl With Cheratussin

Taking Benadryl with Cheratussin (guaifenesin and codeine) can lead to CNS depression. CNS depression can increase the risk of having difficulty breathing and make you extremely drowsy and confused. In severe cases it could lead to coma. It is recommended to avoid taking this combination of drugs in order to prevent these serious side effects from occurring. If you are going to take them you should separate them by 10-12 hours.