Garlic + C, Horseradish, Fenugreek & Marshmallow Tablets

Garlic is well tolerated and does a few small, useful things. These are the questions our naturopaths ask in store, which are mostly about matching the form to what you want.

A good fit if

• You want winter immune support and you'll take it right through the season
• You're after general heart and cholesterol support and you know the effect is small
• You're happy to take it for months rather than weeks
• You want aged garlic extract specifically, which is the form used in the immune trial

Check with us first if

• You take warfarin or another blood thinner. Garlic may add to the effect, and the evidence is mixed on which way it goes.
• You take antiplatelet medicine or have a bleeding disorder.
• You have surgery coming up. The published advice is to stop high doses 7 to 10 days beforehand.
• You take diabetes medicine, because garlic lowers fasting blood sugar on its own.
• You take HIV medicine. Garlic reduces the effect of saquinavir.
• You're pregnant or breastfeeding. There's no evidence either way for this yet.
• It's for a child. The permitted cold and flu wording comes with its own label statement for adults only or children under 2.

• Fresh clove (item 2307). Best known for: Eating it as food, and the reference point for dose. Absorption: Allicin forms when you crush it, not in the whole clove. Typical use: About 2.7 g a clove. Almost no trials actually used fresh cloves.
• Garlic powder tablets (items 2306, 2308, 2309). Best known for: The most trialled form for cholesterol and heart support. Absorption: Usually standardised to how much allicin it can produce. Typical use: 900 mg a day is roughly one clove. This is also the form used in both well-run trials that found no effect.
• Aged garlic extract. Best known for: Where the evidence on immunity and cold severity comes from. Absorption: Ageing turns the harsh sulfur compounds into water-soluble S-allyl-cysteine. Typical use: 2.56 g a day in the cold-season trial. It is not a Schedule 1 name, so it falls under items 459, 2306 or 2307.
• Aged black garlic. Best known for: A milder taste, with the same S-allyl-cysteine marker. Absorption: Aged with heat and humidity. Typical use: One triple-blind trial, with small effects, in people already on medication.
• Garlic oil (item 2310). Best known for: A separate ingredient, made by steam distillation. Absorption: Contains allyl sulfides rather than allicin. Typical use: This is the form with the documented liver enzyme interaction: it slowed CYP2E1 by about 22% in older volunteers.
• Odourless or deodorised. Best known for: Sticking with it for months. Absorption: We found no trial comparing how much allicin it releases with plain products. Typical use: They exist because many people find raw garlic hard to tolerate. We can't tell you they work as well.
• Wild garlic (Allium ursinum, item 461). Best known for: A different species entirely. Absorption: It has its own separate entry. Typical use: Garlic evidence does not carry over to it.

Reference values. There's no recommended intake for garlic. It's a food and a herb rather than a nutrient, so the NHMRC doesn't set one.

Typical supplemental range. Trials have used anywhere from 80 mg to 4,000 mg a day, for 2 to 24 weeks. The cold-season trial used 2.56 g a day of aged garlic extract for 90 days. Most cholesterol trials used 900 mg a day of garlic powder, which that research put at roughly one fresh clove.

Upper level. Australia's permitted ingredients list (Schedule 1) sets no daily maximum for garlic, and there's no NHMRC upper limit. The highest dose used in the trials we looked at was 4,000 mg a day.

Worth knowing. One review found the cholesterol effects were clearer with lower doses taken for longer, so think months rather than megadoses. We haven't checked every Australian label against the trial doses, so we can't tell you a given product matches them. What you need depends on your age, diet and health, so talk to one of our naturopaths.

Food first, where the diet allows it.

• Fresh garlic clove: about 2.7 g; 900 mg of garlic powder was described in trial as equivalent to roughly one clove
• Other allium vegetables (onion, leek, chives): separately scheduled ingredients; studied as a dietary category for cancer risk with a null result

If any of these sound like you, talk to one of our naturopaths or your doctor before you start.

• You take blood thinners such as warfarin. Garlic may strengthen the effect. One review of trial data found no significant change in how the body handles warfarin, while another review of case reports found lower warfarin levels. The evidence conflicts, so this is one for your prescriber.
• You take antiplatelet medicines, or you have a bleeding disorder. Garlic can affect platelets and blood clotting.
• You have surgery coming up. Published clinical advice is to stop high doses 7 to 10 days beforehand, because garlic can make you bleed for longer.
• You take HIV medicines. Garlic makes saquinavir less effective.
• You take medicines that lower blood sugar, including chlorpropamide. Low blood sugar from the combined effect has been reported, and garlic lowers fasting glucose and HbA1c on its own.
• Allergy. Allergic skin reactions (contact dermatitis), hives, swelling (angioedema), pemphigus, anaphylaxis and light-triggered allergy (photoallergy) have all been recorded, though rarely.
• Never put fresh garlic on your skin, especially under a dressing. It causes chemical burns.
• You take medicines where the dose has to be exact (narrow therapeutic index), such as ciclosporin and digoxin. Garlic oil specifically slowed the liver enzyme CYP2E1 by about 22% in older volunteers.
• Breastfeeding. Garlic in a mother's diet changes how a baby behaves at the breast. We found no safety data on pregnancy or breastfeeding either way.
• Everyone. Bad breath and body odour are the most consistently reported complaints in trials, along with rash.