Garlic: overview, benefits, dosage, side effects

Find out all about garlic, including what it does, the benefits of taking it and how much you might need

Written by Jack Feeney on December 18, 2018
Reviewed by Fiona Hunter on January 4, 2019

Overview

What is garlic and what does it do?

Garlic is the edible bulb of a plant, which is part of the lily family,¹ but it’s more than just a kitchen herb with a strong taste and flavour. In fact, garlic has been used as a traditional herbal medicine in ancient civilisations such as Egypt, Greece and Rome. Originally, garlic was used as a performance-enhancer and even given to the first Olympians in Greece, presumably to give them a boost.²

Nowadays, modern scientists agree that garlic is important for health. According to the EU Herbal Medicines Agency, garlic can:

• help prevent hardening of the arteries
• relieve symptoms of colds³

Garlic is available as capsules. Some have been deodorised or have a coating to prevent giving your breath that tell-tale garlic odour.

What does garlic do in the body?

Garlic contains alliin, a compound that converts to a sulphur compound called allicin when it’s cut or crushed. Allicin is considered one of garlic’s most important active compounds, and it’s what gives garlic that distinctive taste and smell.⁴

Scientists think allicin is antibacterial and anti-fungal.⁵ Research has found the following effects of garlic in the body:

It can help prevent hardening of the arteries – a 2013 Iranian study found that compounds in garlic, including allicin, can help prevent fatty deposits in arteries by:

• reducing the amount of fat in the blood
• curbing cholesterol’s tendency to lay down fatty deposits in the arteries⁶

However, other scientists have reported that the cholesterol reduction in the blood may not be signifcant.⁷

Garlic could reduce the length of a cold – few scientific studies have looked into the effects of garlic on the common cold, but a 2001 study in Advances in Therapy reported that people taking garlic supplements were less likely to catch a cold, and also recovered faster if infected.⁸ A 2014 Cochrane review of studies reached the same conclusion, but said more studies were needed to confirm the results.⁹

Dosage

How much garlic is safe to take?

There is no reference nutrient intake (RNI) for garlic. However, it’s safe to consume at normal levels found in your food.¹⁰  If taken medicinally, 1-2 cloves of fresh garlic a day is safe.¹¹

The European Medicines Agency recommends:

• 900-1380mg of garlic powder per day for artery health, or
• 100-400mg a day for coughs and colds protection¹²

The following groups should be careful of taking garlic supplements:

• people having surgery within seven days – there is a risk of bleeding after the operation
• children and young people under the age of 18 years – this has not been proven safe
• women who are pregnant or breast-feeding – garlic supplements have not been proven safe
• anyone taking certain medicines, in particular anti-coagulation or anti-platelet medication – garlic supplements may affect how quickly your blood clots, so speak to your doctor before use¹³

Side-effects

What are the side-effects of taking garlic supplements?

Some common side-effects¹⁴ include:

• breath and body odour
• stomach pain and bloating
• headache and dizziness
• allergic reactions, such as contact dermatitis or conjunctivitis

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Advice is for information only and should not replace medical care. Please check with your GP before trying any remedies.

Sources
1. HSIS. Garlic (Allium sativum)
2. Rivlin RS. Historical Perspective on the Use of Garlic
3. European Medicines Agency. European Union herbal monograph on Allium sativum L., bulbus
4. As Source 1
5. Mikaili P, et al. Therapeutic Uses and Pharmacological Properties of Garlic, Shallot and Their Biologically Active Compounds
6. As above
7. National Center for Complementary and Integrative Health. Garlic
8. Josling P. Preventing the common cold with a garlic supplement: a double-blind, placebo-controlled survey
9. Cochrane. Garlic for the common cold
10. As Source 7
11. As Source 1
12. As Source 3
13. As Source 3
14. As Source 3