There are big bucks to be made selling cold and flu remedies. Last year, Kiwis forked out $38 million at the supermarket on pills and potions for fighting winter bugs.

We looked at more than 50 cold and flu products, from decongestants and antihistamines through to cough drops, to find which offer the most effective relief from winter ills. Considering the hefty price of some products, you might think there’s strong science supporting their effectiveness. But we found it’s often less than convincing.

Oral decongestants

With pseudoephedrine absent from the shelves since 2011, there’s just one decongestant ingredient in cold and flu tablets and elixirs – phenylephrine.

It’s frequently combined in a tablet with paracetamol and marketed under a variety of names, including Codral Relief, which claims to have “a non-drowsy formula for relief of headaches and fever, blocked and runny nose, body aches and pain”.

Three US clinical trials published in the past decade concluded phenylephrine was no better at relieving congestion than a placebo.

Lemsip touts its Cold & Flu with Decongestant capsules as “a quick way to get effective relief from symptoms such as headache, body aches, blocked nose, fever, and sore throat”.

Manufacturers’ claims that phenylephrine may clear congestion date to trials done 40 to 60 years ago. But only half of these trials showed phenylephrine was effective. Three US clinical trials published in the past decade concluded it was no better at relieving congestion than a placebo.

There’s more evidence the paracetamol will relieve your bunged-up nose than the decongestant. You’ll also save money by sticking with the medicine-cabinet staple. A 2-pill dose of the painkiller-decongestant tablets we looked at were, on average, 3 times the price of plain paracetamol.

When we asked companies for evidence to support claims for phenylephrine, the results were underwhelming.

The New Zealand Self Medication Industry Association (NZSMI) – the PR representative for major maunfacturers such as Reckitt Benckiser (Nurofen, Lemsip) and Bayer (Demazin) – offered a decade-old study showing phenylephrine working in 4 out of 8 trials.

Others pointed to Medsafe’s registration of the ingredient for use as a decongestant. Multichem (which produces the Ethics range) ignored our requests.

No company alerted us to the recent US clinical trials showing phenylephrine was no more effective than a placebo at relieving congestion. Even Bayer, which sells Demazin-brand medicines with phenylephrine and which sponsored 2 of the studies, didn’t mention them.

Bottom line: Good evidence is yet to emerge supporting phenylephrine’s effectiveness as a decongestant.

Cough medicines

Cough medicines fall into 2 categories: dry cough remedies, which use a cough suppressant such as dextromethorphan or pholcodine, and chesty cough remedies, which typically use the expectorant guaifenesin.

If you’re suffering from a dry cough, Vicks Formula 44 Dry Cough promises “long-lasting cough relief”, while Duro-Tuss Forte says it “relieves a stubborn dry cough”.

Independent reviews have found little if anything to support the claims for cough medicines.

On the chesty side, Benadryl Chesty Cough & Nasal Congestion says it will “relieve chesty coughs … fast”. Robitussin’s Chesty Cough formulation “loosens and helps clear chest congestion”, according to the box.

However, independent reviews have found little if anything to support the claims for these ingredients. A 2014 study by the Cochrane Collaboration, which conducts systematic reviews on healthcare, cautiously concluded there was “no good evidence for or against” their effectiveness.

The review also questioned how the products “can continue to be promoted using language that implies that their effectiveness is not in doubt”.

In support of product claims, the NZSMI and Procter & Gamble (Vicks) sent us a study on dextromethorphan, which concluded more research into the active ingredient’s effectiveness is a good idea. They also sent us research where artificially stimulated coughs were successfully suppressed.

Radiant Health, which sells pholcodine in the Duro-Tuss range it distributes, pointed to a 2012 European Medicines Agency review that noted there was “a large body of data demonstrating the effectiveness of opioids in the management of non-productive cough”. However, Cochrane Reviews have not found the evidence conclusive for pholcodine.

Six recent international clinical trials on over-the-counter cough formulations containing dextromethorphan or guaifenesin also did not demonstrate they work. That’s despite their high price: products we looked at ranged from $12.99 to $28.99.

GlaxoSmithKline (Panadol, Coldrex), Pfizer (Dimetapp, Robitussin), Procter & Gamble and Reckitt Benckiser (Mucinex, Strepsils) all sponsored at least one of these studies but none mentioned them in replies to us.

The only ingredient for which studies show some support is the expectorant bromhexine, found in some Benadryl, Bisolvon, Dimetapp, Duro-Tuss and Robitussin formulations. However, evidence for its effectiveness is largely based on trials involving people suffering from long-term respiratory disease rather than a winter bug.

Bottom line: If you’re considering a cough medicine, keep an eye on the ingredients and be aware that you may be getting nothing beyond the placebo effect.

Double dosing

The same ingredients pop up repeatedly with over-the-counter cold remedies, which places consumers at risk of double or triple-dosing.

For example, if a patient took 2 capsules of Codral’s Cold, Flu & Cough Day or Night, a dose of Vicks Formula 44 Dry Cough Syrup and followed it with a Strepsils Dry Cough Lozenge, they would receive the drug dextromethorphan in 3 ways.

Overuse of the medication can cause breathing problems, vomiting and convulsions.

Too much paracetamol is also risky and can lead to liver failure. Paracetamol is commonly found in cold and flu sachets, such as Lemsip and Codral Relief varieties.

Bottom line: Always check the list of active ingredients before you buy – and take – over-the-counter medication. Medsafe requirements mean many over-the-counter products must carry a warning about the risks of taking more than one medicine at a time.

Antibacterial and antiviral action

A standard cold or bout of flu is caused by a virus, not bacteria. But that hasn’t stopped manufacturers adding antibacterial agents and spruiking their benefits.

Lozenges

The Strepsils range boasts on packs it has “double antibacterial action”. Ethics Medicated Throat Lozenges uses the same phrase, and emphasises the product provides “symptomatic relief of sore throats and mouth infections”. Codral and Difflam also sell lozenges touting the antibacterial agents in them.

While sucking a throat drop will increase the flow of saliva and soothe your throat, you’d get the same effect from a lolly or a spoonful of honey. The anti-inflammatory and anaesthetic agents in some products may numb a painful throat, but their antibacterial ingredients won’t do anything to help cure your cold.

Despite the antibacterial hype on the front of the packs, the Codral and Strepsils ranges have a disclaimer on the back that states, “the efficacy of an antibacterial agent in lozenges in reducing the severity or duration of throat infections has not been clinically established”. Difflam packs carry a similar warning, but Ethics brand lozenges stay mum.

Hand washes

There’s little point buying products such as antibacterial hand washes if you’ve got a cold or flu. According to the US Centers for Disease Control and Prevention (CDC), it hasn’t been proved these hand washes are any better at stopping the spread of infection than similar products without antibacterial chemicals.

There’s also a risk they could do harm. The CDC says laboratory tests have shown a link between antibacterial chemicals in cleaning products and bacterial resistance. However, further research is needed to determine whether these products may contribute to bacterial resistance outside of the lab.

Antiviral tissues

Feel free to stick with regular tissues. The idea of a 3-ply tissue with a middle layer of citric acid and sodium lauryl sulfate to kill viruses was first put to the test in a series of trials in the 1980s. The results were disappointing – the technique managed to cut down transmission from one person in the house to another, but overall these families still caught just as many colds as the ones using tissues with a placebo.

The tissues can cost up to 4 times the price of others. Regular hand washing with soap and water, in and away from the home, and covering your mouth when you cough or sneeze are the best techniques to prevent transmission of common cold germs. The vaccine remains your best bet for avoiding the flu.

Bottom line: Antibacterial and antiviral additives will do little to prevent you from catching a cold, or relieve your symptoms once you have one.

Natural remedies

Vitamins and extracts are often promoted as being able to both prevent the common cold as well as shorten the length of time you’re sick. But the jury’s still out on most products.

Probiotic supplements

There are signs regular use of “good bacteria” may ward off illness and help a person recover more quickly. A 2015 Cochrane Review found taking a probiotic supplement in a tablet or dairy product appeared to halve the number of colds a person had and cut the duration of these bugs by nearly 2 days. However, the experts had misgivings about the quality of the trials and considered the evidence low.

Garlic

The herb is often found in supplements purporting to boost the immune system. But systemic reviews have found only one good-quality study showing garlic supplements lower a person’s risk of developing a cold. More research is needed.

Vitamin C

Research has failed to demonstrate the vitamin offers any benefit in either prevention or treatment of winter bugs, beyond that of the placebo effect. The sole exception is for people under physical stress, such as high-performance athletes.

Echinacea

There is some evidence that regular use of these supplements can slightly reduce the risk a person will experience a cold. However, this benefit appears to be weak.

Bottom line: There’s no good evidence showing regular use of supplements will reduce your chances of catching a cold. Product claims for supplements have leapt ahead of the science.

What may work

There are cold and flu remedies that have better evidence behind them. And they’re often cheaper options.

Nasal sprays

The blood vessels in your nose swell up when you catch a virus, contributing to that “bunged up” feeling, alongside the extra mucus your body produces. Nasal sprays encourage these blood vessels to constrict or nasal glands to reduce the mucus produced. Studies suggest sprays with ipratropium bromide, such as Atrovent Nasal and Otrivin Plus, may offer relief from congestion, while oxymetazoline, used in Dimetapp, Drixine, Sudafed and Vicks Sinex, and xylometazoline, used in Otrivin, may also provide relief, albeit modest. Nasal sprays are also cheaper than painkiller-decongestant pills. The downside of nasal sprays is that you must stop using them after a certain time (usually 3 to 5 days) or risk “rebound congestion”, when a blocked nose returns after you cease using the product.

Antihistamines

Some over-the-counter cold and flu tablets combine paracetamol with an antihistamine and a decongestant. Antihistamines appear to offer some cold sufferers a short-term boost. As they do for allergy sufferers, antihistamines block the body chemical histamine, which causes runny noses, watery eyes and sneezing. If you choose an ordinary antihistamine pill you’ll pay, on average, $1.51 a day, compared with $5.40 for combination cold pills with an added antihistamine.

Paracetamol, ibuprofen and aspirin

These everyday painkillers can offer relief from the aches and discomfort of winter bugs.

Honey

The jury is still out but there are small studies that have found honey can relieve symptoms and help children sick with the common cold sleep better.

A doctor’s note

University of Auckland medical professor Bruce Arroll says the best thing you can ask your doctor for is a sick note instructing you to take a few days off work. This stops you passing the virus to the outside world. There’s no cure for the common cold and most prescription medicines won’t offer anything more than a placebo effect.

Bottom line: A few days of R&R remains the best prescription for recovery. Your cold should clear up within a week, though a cough may last a month. Flu can linger up to a fortnight. If your symptoms are severe, see a doctor.

GUIDE TO THE GRAPHICS PRICE is based on the recommended dose of a medication or combination, and averaged across a range of brands. Prices were collected in a store survey conducted in March 2017.