Cold, Cough, and Flu Medicines

TL;DR. Most of what is sold for colds does very little, and the combination products are the main route to accidental paracetamol overdose. Oral phenylephrine, the decongestant that replaced pseudoephedrine in most pharmacy products, was judged ineffective by an FDA advisory committee in 2023 because it is almost entirely destroyed by the liver before reaching the nose. Cough medicines have poor evidence and honey has better. Antibiotics do nothing for a cold, which is a virus. The things that genuinely help are unglamorous: rest, fluids, paracetamol or ibuprofen for symptoms, saline, steam, and honey.

1. What a cold actually is

Over 200 viruses cause the common cold, with rhinoviruses accounting for roughly half. Influenza, RSV, coronaviruses (including SARS-CoV-2), and others cause overlapping illnesses.

Most cold symptoms are your immune response, not the virus. The runny nose, congestion, sore throat, and malaise come from inflammatory mediators released as your immune system responds. This is why symptomatic treatments work by suppressing that response, and why fever, within reason, is functional rather than something to eliminate.

Typical course: incubation 1 to 3 days, peak symptoms days 2 to 3, resolution 7 to 10 days, cough often lasting 2 to 3 weeks. A cough persisting three weeks after a cold is normal, and this is one of the more useful things to know, because it prevents unnecessary antibiotic requests.

Don't be confused: a cold and flu are different illnesses. A cold comes on gradually with nasal symptoms and you can usually function. Influenza comes on abruptly with high fever, severe muscle aches, headache, and profound fatigue, and typically puts you in bed. "Man flu" is almost always a cold; genuine influenza is unmistakable to anyone who has had it.

2. The ingredients, one by one

Every cold and flu product is a combination of a small number of ingredients. Learn them and the shelf becomes simple.

Analgesic / antipyretic

Paracetamol or ibuprofen. These genuinely work for the headache, sore throat, aches, and fever, and they are the main reason cold remedies help at all.

This is where the danger is. If you take a cold and flu sachet containing 1,000 mg of paracetamol, and separately take paracetamol for a headache, you can exceed the 4 g daily maximum without noticing (Chapter 65). Check every box.

Decongestants

Alpha-adrenergic agonists that constrict blood vessels in the nasal mucosa, reducing swelling.

Rhinitis medicamentosa is the reason for that limit. Using a topical decongestant spray for more than about five days produces rebound congestion: the mucosa becomes dependent, and stopping causes worse blockage than the original illness, which drives further use. Breaking the cycle requires stopping, sometimes with a short course of steroid nasal spray, and takes days of discomfort.

Cautions for oral decongestants: they raise blood pressure and heart rate, so avoid in uncontrolled hypertension, heart disease, and hyperthyroidism; they can cause insomnia and agitation; they interact dangerously with MAOIs; and they can precipitate urinary retention in men with prostate enlargement and worsen glaucoma.

Antihistamines

First-generation antihistamines (chlorphenamine, diphenhydramine, promethazine, doxylamine) appear in night-time cold products. Their effect on a cold is largely anticholinergic drying plus sedation, not antihistamine action, because a cold is not an allergic condition.

They do produce a modest reduction in runny nose and sneezing in the first couple of days, and they make you drowsy, which is the actual selling point of "night" formulations.

Second-generation antihistamines (loratadine, cetirizine) do essentially nothing for a cold, because they do not cross into the brain and colds are not histamine-mediated.

Cough medicines

The evidence here is poor across the board. Cochrane reviews of over-the-counter cough preparations for acute cough have consistently concluded there is no good evidence for or against their effectiveness.

Honey is the standout. A Cochrane review found honey more effective than no treatment, placebo, and diphenhydramine for cough in children, and comparable to dextromethorphan. It is cheap, palatable, and safe.

Honey must not be given to infants under 12 months, because of the risk of infant botulism from Clostridium botulinum spores, which an immature gut cannot handle.

Cough and cold medicines are not recommended for children under 6 in the UK, US, and elsewhere, following reviews that found no evidence of benefit and reports of serious harm including deaths from overdose. For ages 6 to 12 they are advised only on pharmacist advice. This restriction is widely unknown.

The rest

• Caffeine in some products, to offset sedation and slightly enhance analgesia.
• Menthol and eucalyptus in rubs, inhalations, and lozenges. Menthol activates cold receptors (TRPM8), producing a sensation of easier breathing without measurably improving airflow. That is not nothing: perceived breathing improves and it feels soothing.
• Zinc lozenges: reasonable evidence for reducing cold duration by around a day, if started within 24 hours and at high doses. The taste is unpleasant and nausea is common.
• Vitamin C: does not reduce the incidence of colds in the general population; reduces duration by around 8 percent, roughly half a day (Chapter 15).
• Echinacea: inconsistent trials, no reliable effect.

3. What actually helps

Ranked by evidence:

1. Paracetamol or ibuprofen for fever, aches, and sore throat.
2. Fluids and rest. Unglamorous, and the mainstay.
3. Honey for cough, in anyone over 12 months. A teaspoon, in warm water or lemon if you like.
4. Saline nasal irrigation or spray. Genuinely useful, especially for congestion and in children, and free of side effects.
5. Steam inhalation. Evidence is weak and it is soothing. Do not use boiling water with children: scalds from steam inhalation are a documented paediatric injury.
6. Topical decongestant spray for up to 3 to 5 days if congestion is preventing sleep.
7. Pseudoephedrine if you can get it and have no contraindication.
8. Zinc lozenges started very early.
9. Menthol for perceived relief.
10. Sleep, which is genuinely immunologically important.

Chicken soup has a small literature suggesting mild anti-inflammatory effects and it is warm fluid and salt, which is most of the benefit. There is no reason not to.

4. What does not help

• Antibiotics. A cold is a virus. Antibiotics do nothing, cause side effects, disrupt the gut microbiome, and drive resistance (Chapter 72). Green or yellow mucus does not indicate bacterial infection: the colour comes from neutrophil myeloperoxidase and is a normal part of viral infection.
• Oral phenylephrine, on current evidence.
• Most cough syrups, beyond their demulcent effect.
• Cold and flu products in children under 6.
• Vitamin C started after symptoms begin, which does not shorten a cold at all; only regular prior supplementation has the small effect.

5. When it is not just a cold

See a doctor or seek urgent care if:

• Difficulty breathing, chest pain, or you cannot complete a sentence
• Fever above 38 °C in a baby under 3 months, or any unwell young infant
• Symptoms lasting more than 10 days without improvement, or improving and then getting distinctly worse (the classic pattern of a secondary bacterial infection)
• Severe headache with neck stiffness, rash that does not fade under pressure, photophobia, or confusion: possible meningitis
• Severe sore throat with drooling, difficulty swallowing, or inability to open the mouth
• Symptoms in someone immunosuppressed, pregnant, very elderly, or with significant lung or heart disease
• Coughing blood, or a cough lasting more than 3 weeks that is not improving

Influenza antivirals (oseltamivir/Tamiflu, zanamivir) reduce illness duration by roughly a day if started within 48 hours. Their value in healthy adults is modest and contested; they are more clearly indicated in high-risk groups and in hospitalised patients (Chapter 73).

Vaccination is the intervention that works. Annual influenza vaccination reduces infection, hospitalisation, and death, particularly in older people, pregnancy, and those with chronic conditions (Chapter 74).

6. Practical guidance

• Buy the ingredients separately, not as a combination. Paracetamol when you need pain relief, a decongestant when you are blocked, honey for cough. This avoids taking drugs you do not need and, crucially, avoids double-dosing paracetamol.
• Combination products are convenient and expensive and carry the overdose risk. If you use them, use only one product at a time and read the ingredients.
• Nasal spray decongestants: five days maximum, no exceptions.
• Check labels for paracetamol before adding any other painkiller.
• Do not give cough and cold medicines to under-6s.
• Wash your hands. Rhinovirus transmits substantially by hands and surfaces, and handwashing is among the better-evidenced preventive measures.

7. The bottom line

• Most cold symptoms are your immune response, and most of what is sold to treat them has weak evidence. The analgesic in the packet is doing most of the work.
• Oral phenylephrine appears not to work, and an FDA advisory committee said so unanimously in 2023. Pseudoephedrine does, and is behind the counter.
• Nasal decongestant sprays work well and cause rebound congestion after about five days.
• Cough medicines have poor evidence. Honey beats several of them in trials and must not be given under 12 months.
• Cough and cold medicines should not be given to children under 6.
• Antibiotics do nothing for a cold, and coloured mucus is not evidence of bacterial infection.
• The most dangerous thing in the cold and flu aisle is duplicated paracetamol.

Sources and notes

Doses, cautions, and interactions follow the British National Formulary and the electronic Medicines Compendium; US figures follow FDA labelling. Cold virology and symptom course follow standard infectious disease references. The FDA advisory committee's September 2023 unanimous vote that oral phenylephrine is ineffective at approved doses, and the subsequent proposed order, are in the FDA's Nonprescription Drugs Advisory Committee record; the underlying bioavailability data follow Hendeles and Hatton's work. Rhinitis medicamentosa follows otolaryngology references. Cochrane reviews cover over-the-counter cough preparations (Smith, Schroeder, and Fahey), honey for cough in children (Oduwole et al.), zinc lozenges (Hemila), vitamin C (Hemila and Chalker), and echinacea (Karsch-Volk et al.). The under-6 cough and cold restriction follows MHRA and FDA reviews of paediatric adverse events. Pholcodine withdrawal in 2022 follows the EMA and MHRA reviews of anaphylaxis sensitisation to neuromuscular blockers. Menthol and TRPM8 perceived nasal patency follows Eccles' work. Infant botulism from honey follows CDC guidance. Oseltamivir evidence follows the Cochrane review by Jefferson et al., 2014, and the associated campaign for full clinical study report access.

Open questions. Whether oseltamivir reduces complications and hospitalisation in high-risk groups remains genuinely contested between the Cochrane analysis and observational data. Most over-the-counter cough preparations have never been adequately tested.

👉 Next: allergy medicines.