Mr H I use Garlic in mega doses and suffer no ill health, colds and flu.
The benefits according to the net are :Garlic can be used to treat high cholestrol, parasites, respiratory problems, poor digestion, and low energy. Studies suggest that regularly eating garlic helps lower blood pressure, controls blood sugar and blood cholesterol, and boosts the immune system. It has also been found to reduce the risk of esophageal, stomach, and colon cancer.
And on the flipside is : Raw garlic is very strong, so eating too much could produce problems, for example irritation of or even damage to the digestive tract.
There are a few people who are allergic to garlic. Symptoms of garlic allergy include skin rash, temperature and headaches. Also, garlic could potentially disrupt anti-coagulants, so it's best avoided before surgery. As with any medicine, always check with your doctor first and tell your doctor if you are using it.
Important: Research published in 2001 concluded that garlic supplements "can cause a potentially harmful side effect when combined with a type of medication used to treat HIV/AIDS"
So at the doses you have stated it seems safe but as usual any questions regarding health, medicines, vitamins and herbs etc.. Your best bet is to consult your gp and do some research and make an educated decision based on the facts you receive.