The problem is very few of these products are tested in the same way prescription drugs are reviewed. If they're considered low risk they are listed with the drug regulator, but very few have gone through independent investigation to test the claims they make.

This week the University of Sydney announced it would establish the Maurice Blackmore Chair in Integrated Medicine with the specific role of studying alternative medicine to see whether it worked, how it worked and whether it had any side effects.

But the $1.3 million donation from the vitamin giant to fund the position sparked controversy, with critics warning of the potential for a conflict of interest.

Friends of Science in Medicine president John Dwyer said although he supported research into complementary medicines in principle, "a huge amount" had already been conducted.

"It's a question of whether they work and whether you need them," Professor Dwyer said.

The National Health and Medical Research Council concluded in March there was no health condition where evidence existed that homeopathy was effective.

Because few tests are performed on complementary medicines, it can be hard for the public to discern which products work versus those that are a waste of money. One source of credible information are the reviews conducted by organisations such as the Cochrane Collaboration. They consider all the available evidence for a given supplement or alternative medicine, assess how reliable that evidence is, and then make a statement about its efficacy.

Three complementary therapies with evidence that they work:

St John's wort for depression

St John's wort is the common term for extract of hypericum perforatum, which has shown to be an effective treatment for mild to moderate depression in several published trials.

A 2010 study published in European Neuropsychopharmacology demonstrated some compilations of the herb were significantly better than a placebo for the treatment of depression and had fewer side effects than standard drugs.

But the preparation of the herb varies and not all formulations have been proven to be effective.

A 2005 Choice investigation invited the 27 Australian sponsors of St John's wort products to provide scientific evidence to back up their advertising claims, but only 14 agreed to do so.

Among them, six were able to provide convincing evidence with a clear link between their own product and the one that had been tested in clinical trials.

These were the Chemist's Own, Flordis Remotiv, Guardian Pharmacies, Herron, Hilton Healthstream and Mediherb products.

Vitamin D for pregnant women and the elderly

Vitamin tablets are a poor substitute for a balanced diet, but there are times of life when these supplements are beneficial.

It is often recommended to pregnant women, who are at a higher risk of developing vitamin D deficiency, and elderly people, who have less exposure to sunlight, to prevent them from breaking bones.

A Cochrane review of five studies indicated that pregnant women who took Vitamin D had higher levels of Vitamin D at term, but there was no evidence that it prevented pre-eclampsia, gestational diabetes, impaired glucose tolerance, caesarian section or death in the mothers.

It had little or no effect on the babies.

Another study found that post-menopausal women and older men were less likely to suffer hip fractures if they took Vitamin D with calcium supplements.

Monash University public health researcher Ken Harvey said fresh fruit and vegetables had more vitamins than supplements.

African geranium for treating cold symptoms

African geranium the common name for Pelargonium Sidoides, a plant native to South Africa, that is used to treat bronchitis, sinusitis and the common cold.

The herbal extract of the plant is known as Umckalaobo and it is available in liquid and tablet form.

There is a body of evidence to show that it relieves symptoms such as headaches, nasal discharge and coughing in certain formulations, with no serious side effects.

But a Cochrane review of the studies indicated that the quality of evidence in all the studies was low. A version of the product is available in Australia as Kaloba oral liquid.

Three complementary medicines with little or no evidence they work:

Vitamin C for treating and preventing a cold

There's no denying that vitamin C is vital for your body's growth and repair.

As an antioxidant, it travels around the body mopping up some of the damaging byproducts of ageing, smoking and infections. While the vitamin is considered an essential nutrient, many people take daily supplements hoping it will ward off a cold.

Unfortunately the most reliable evidence says you're wasting your money. A review of 29 studies, which compared people who took Vitamin C to those who took a placebo, found regular vitamin use did not reduce a person's number of colds.

Echinacea for treating and preventing a cold

Echinacea is the general name for a group of plants that can be sold in a variety of forms, from different species to different parts of the plant, to prevent or treat a common cold.

Because these products can be prepared in many ways it's hard to find conclusive evidence that all these products definitely don't work, but most scientific studies have found it is ineffective. A review of 12 studies found a very small preventive benefit, but none of the results were considered statistically significant, meaning the effect may have just happened by chance.

Studies that looked at whether echinacea could reduce the severity of a cold had mixed results. Two trials found the treatment was slightly better than a placebo while four others found no effect.

Ginseng for improving brain function

This herb is one of the most popular Chinese medicines in the world. Like echinacea it's a number of closely related plants. Many people take it hoping it may improve their brain function and stave off ageing. It has also been promoted as a treatment for dementia. But there's little reliable evidence to support it doing either of those things.

Like many complementary medicines, good quality studies – where the treatment is compared to a placebo – have not been conducted with large groups of people. Ginseng is no different. A review of several studies found there was no convincing evidence to show ginseng improved brain function. Most of the studies were small and the tests measuring attention and concentration were inconclusive. The same authors also concluded there was no high-quality evidence about its efficacy in patients with dementia.