What’s Really in Your Cold Medicine?

You know that moment when your nose is stuffy, your throat’s scratchy, and your head feels like it’s stuffed with cotton balls? You stumble to the pharmacy, grab a cold medicine, and hope for the best. But have you ever actually looked at what’s in those pills or syrups?

Most over-the-counter (OTC) cold meds in the U.S. aren’t curing your cold (since it’s viral), but they do help you feel a lot better while your body fights it off. The key is knowing what each ingredient does and what side effects to watch for.

1. Acetaminophen (aka Tylenol)^[1]

Purpose: Reduces fever and relieves mild to moderate pain.
Found in: DayQuil, Tylenol, NyQuil, Theraflu, Robitussin Multi-Symptom.
How it feels: Helps you power through work when you’re achy and burning up.
Possible side effects:

• Liver damage (especially if you exceed 3,000–4,000 mg/day)
• Rare allergic reactions (rash, itching)
• Nausea

🔸 Real talk: I once took two different cold meds without checking, they both had acetaminophen. Learned the hard way to always read labels.

2. Dextromethorphan (DM or DXM)^[2][3]

Purpose: Suppresses cough by acting on the brain’s cough center.
Found in: Robitussin DM, Delsym, NyQuil, DayQuil, Theraflu.
How it feels: That dry, hacking cough? Silenced.
Possible side effects:

• Drowsiness
• Dizziness
• Confusion (especially in high doses)
• Upset stomach

❗ Important: Some teens misuse DM for a “high.” Taking too much can be dangerous, even fatal.

3. Guaifenesin^[4]

Purpose: Expectorant — loosens mucus in the lungs.
Found in: Mucinex, Robitussin Cough and Chest Congestion, Theraflu Cough Relief.
How it feels: Helps turn that tight chest cough into a productive one.
Possible side effects:

• Diarrhea
• Nausea or vomiting
• Headache
• Dizziness
• Hive
• Skin rash
• Rare stomach upset

💧 Tip: Drink lots of water with it, it works better when you’re hydrated.

4. Phenylephrine^[5][6]

Purpose: Nasal decongestant. Shrinks blood vessels in the nose to relieve congestion.
Found in: DayQuil, Sudafed PE, Tylenol Sinus, Mucinex Sinus-Max.
How it feels: Clears your sinuses — kind of.
Possible side effects:

• Increased blood pressure
• Nervousness or jitteriness
• Trouble sleeping

🧠 Note: In 2024, the FDA reviewed phenylephrine’s effectiveness and found it may not work as well as we thought, especially in pill form.^[7]

5. Pseudoephedrine^[8]

Purpose: Powerful nasal decongestant, similar to phenylephrine but more effective.
Found in: Sudafed, Advil Cold & Sinus, Allegra-D, Claritin-D.
How it feels: Like someone finally opened your airways.
Possible side effects:

• Insomnia
• Anxiety
• Irregular or slow heartbeat
• Increased blood pressure(in high doses)

⚠️ Heads-up: You’ll have to ask for this at the pharmacy counter (and show ID). It’s regulated because it can be used to make methamphetamine.^[9]

6. Diphenhydramine^[10]

Purpose: Antihistamine that makes you drowsy. Used for runny nose, sneezing, and allergy symptoms.
Found in: Benadryl, Tylenol PM, ZzzQuil, NyQuil.
How it feels: You’ll probably get some sleep.
Possible side effects:

• Drowsiness (major!)
• Dry mouth, nose, and throat
• Nausea
• Headache
• Excitement (especially in children)

🌙 Tip: Great for nighttime relief, but don’t mix with alcohol or other sedatives. Remember that alcohol can add to the drowsiness caused by this medication. Avoid alcoholic beverages while you are taking this medication.

7. Chlorpheniramine^[11]

Purpose: Another antihistamine for sneezing, watery eyes, and itchy throat.
Found in: Coricidin HBP, NyQuil, Alka-Seltzer Plus.
How it feels: Helps calm allergic reactions and colds with allergy-like symptoms.
Possible side effects:

• Drowsiness
• Dry mouth, nose, and throat
• Nausea
• Vomiting
• Headache

🧓 Chlorpheniramine is an antihistamine that reduces the natural chemical histamine in the body.^[12]

Other Ingredients to Know

• Zinc: May shorten cold duration slightly if taken early, but can cause nausea and a bad taste.
• Vitamin C: No strong evidence it prevents colds, but some feel it shortens them.
• Honey & Menthol: Found in natural or herbal cold remedies, great for soothing sore throats and coughing, but not FDA-regulated as drugs.

Read Before You Pop That Pill

👉 Always check active ingredients, many cold medicines combine 3–5 drugs in one.
👉 Don’t double up on different brands unless you know what’s in them.
👉 If you have high blood pressure, heart disease, or are on other meds, talk to a pharmacist or doctor first.
👉 And if symptoms last more than 10 days or suddenly worsen, see a doctor.

References

• [1] Mayoclinic, Acetaminophen (oral route, rectal route)
• [2] MedlinePlus, Dextromethorphan
• [3] National Library of Medicine, Dextromethorphan Toxicity
• [4] Mayoclinic, Guaifenesin (oral route)
• [5] National Library of Medicine, Phenylephrine
• [6] MedlinePlus, Phenylephrine
• [7] FDA, FDA Proposes Ending Use of Oral Phenylephrine as OTC Monograph Nasal Decongestant Active Ingredient After Extensive Review
• [8] Mayoclinic, Pseudoephedrine (oral route)
• [9] FDA, Legal Requirements for the Sale and Purchase of Drug Products Containing Pseudoephedrine, Ephedrine, and Phenylpropanolamine
• [10] MedlinePlus, Diphenhydramine
• [11] MedlinePlus, Chlorpheniramine
• [12] Drugs.com, Coricidin

Useful Resource

• What Cold Viruses Are Circulating in 2025? Symptoms & Treatment