When you're in the grip of a phlegm-fuelled misery fest, you can start to feel a little desperate for any sort of relief.
Take a squiz at the vitamin and supplement shelves at the supermarket, or browse the chemist aisles, and you'll find plenty of things promising a solution.
But before you make a purchase, you should know that some of these "solutions" are backed by a lot more evidence than others.
Vitamins and supplements are regulated
But before we look at how the science works, it helps to understand how 'medicines' are regulated in Australia.
In a nutshell, not all medicines undergo the same level of scrutiny or oversight. So even though vitamin C might sit next to a cold and flu medication on the shelf, they don't necessarily undergo the same scrutiny.
Complementary medicines and supplements, which include vitamins, minerals, herbal, aromatherapy and homeopathic products, are in a different category to more conventional medicines, such as prescription drugs or over-the-counter medications.
In Australia, all medicines are regulated by the Therapeutic Goods Administration — under which drugs can be categorised as registered (AUST R) or listed (AUST L).
Registered medicines, including prescription medications (e.g. antibiotics) and over-the-counter medications (e.g. painkillers), are "assessed by the TGA for quality, safety and efficacy".
Most complementary medicines are listed, meaning that while they have to meet some safety and hygiene standards, they don't have to meet the same strict efficacy or effectiveness standards that registered medicines do.
This means complementary medicines might not come with the same effectiveness as your conventional medicines.
However, like conventional medicines, they can come with possible side effects.
You can also overdose on some of them and they can interact with other medicines you take.
These risks are greater for certain people, such as those with pre-existing health conditions or pregnant or breastfeeding women.
"Safety is a relative thing," explains clinical pharmacology professor Ric Day, from St Vincent's Hospital in Sydney.
"If you are treating someone with a serious illness you'd perhaps tolerate more serious side effects than if you're treating someone with a one-off headache."
The bottom line: it's always a good idea to check with your pharmacist or your GP before taking any sort of medication, including vitamins or supplements.
So, what's the low-down on cold-busting complementary medicines?
Eating a diet rich in fruits and vegetables is the best way to not only get your vitamin C, but the other numerable benefits that come with a balanced diet, too.
If you're finding it tough to get plenty of fruit and veg, though, taking vitamin C supplements is an alternative way to work the nutrient into your regime.
As far as protection from colds, taking the supplement hasn't been shown to have any kind of preventative effect. Some studies have shown, however, that if you take it early enough in your sickness, then it can reduce symptoms by up to a day and a half.
Adults only need about 30mg of vitamin C per day — and taking any more than 1g can lead to stomach pains or diarrhoea.
"If you're taking multiple different products with similar ingredients, you can easily go over the recommended limit," explains Nerida Packham, pharmacist and Medicines Line Team lead at NPS MedicineWise.
"Remember to look at the active ingredients."
If you eat meat, fish or dairy, the chances are you're getting plenty of it right there. If you're vegetarian or vegan, it might be worth having a chat with a health professional just to check.
Similar to vitamin C, there is a small amount of evidence that suggests zinc might be able to reduce your cold symptoms by about a day if you take as soon as you start to feel symptoms.
If you're going to give it a go, just be careful to only take the recommended dosage.
Taking too much can lead to deficiencies in other minerals as zinc can affect their uptake by the body, possibly leaving your immune system even worse for wear.
Echinacea is often sold as an "immune-boosting" supplement. But this is even harder to pin down the evidence for than vitamin C or zinc — it's a plant, and different remedies incorporate different parts and different amounts.
There also isn't a particular known active ingredient, which can make it tricky to do quality experiments on.
There are a handful of safety concerns associated with the plant, too. It can bring out rashes in children, trigger allergies in asthma patients and — like many complementary medicines — interact with other drugs.
"It's broken down in the liver, so there is a low risk of it interacting with other medications which are processed there — that includes blood thinners, antidepressants, and some antibiotics," Ms Packham says.
Garlic has long been thought to help with the symptoms of colds and flu.
"There aren't enough clinical trials to provide any solid evidence that it can either prevent colds or treat symptoms," Professor Day says.
Surprisingly, even though garlic is a natural herb, it can have some drug interactions when it's taken in a high amounts in supplement form. These drugs include blood thinners and antivirals.
Don't be shy to ask for advice
Complementary medicines are growing in popularity and you shouldn't feel embarrassed about asking any sorts of questions about them from a health professional.
Of course, there is plenty of information online too, but not all of it is trustworthy.
"You do have to be careful on the internet because there are lot of websites about complementary products but they are often trying to sell them," Ms Packham says.
She advises sticking to reputable websites, like the National Health and Medical Research Council or the US' National Center for Complementary and Integrative Health, or calling MedicineWise.
So, what should you do when you feel a cold or flu coming on?
Unfortunately, there is no miracle cure.
Professor Day recommends taking drugs targeted for specific symptomatic relief.
"For a headache, you would take analgesics so, most commonly, paracetamol. If you want to not be dripping then you can take an antihistamine," he says.
He also emphasises that it's important to get plenty of rest, and stay home if at all possible, as this stops the virus from spreading.
"Just look after yourself a bit more than you normally would. If you're a regular exerciser, then you don't want to be thrashing yourself in the grip of a virus. Take care of yourself, rest, and get plenty of fluid."
This is general information only. For detailed personal advice you should see a qualified medical practitioner who knows your medical history.