They found significant blood pressure falls among participants - with the greatest drops among those who had higher blood pressure readings to begin with.
In some cases, the effects were similar to those achieved with common anti-blood pressure drugs, such as beta blockers and ACE inhibitors, said Dr Karin Ried, of Adelaide University in South Australia.
More than 16million Britons have high blood pressure and many more are thought to suffer from it without knowing. If the condition is not treated, it can lead to heart attacks and strokes. Doctors recommend that sufferers lower their blood pressure by cutting their intake of salt, losing weight and getting fit.
Now the Australian research suggests that extra help is at hand in readily available over the counter garlic supplements.
Dr Ried and her team, writing for the scientific journal BMC Cardiovascular Disorders, said the 600mg to 900mg dosage used in the studies was equivalent to 3.6mg to 5.4mg of garlic's active ingredient, allicin.
A fresh clove of garlic contains 5mg to 9mg of allicin.
More research was needed to determine whether garlic supplements might have a long-term effect on heart disease risk, the researchers added.