Garlic
Herbal products and dietary supplements
Herbal products and dietary supplements
Allium sativum supplements, promoted for cholesterol and blood pressure. Modest lipid effects at best; they can add to bleeding risk.
Also called: Allium sativum, Aged garlic extract
Quick facts
- Group
- Herbal products and dietary supplements
- Target
- Platelets and cholesterol synthesis (allicin and related sulfur compounds)
- Used for
- Promoted for high cholesterol
- Key effects
- Breath and body odour · Abdominal pain
- Monitor
- INR and bleeding signs
No doses: the clinician sets them by the current guideline.
Mechanism of action
Crushing garlic converts alliin into allicin and related organosulfur compounds. In laboratory studies these inhibit HMG-CoA reductase and act as antioxidants; in clinical studies garlic has antiplatelet effects, possibly by reducing thromboxane synthesis. The cholesterol and blood pressure effects in people are small.
- Alliin becomes allicin when garlic is crushed
- Organosulfur compounds reach the blood
- Antiplatelet effect; weak lipid lowering
- Bleeding risk adds up with anticoagulants
Indications
- Promoted for high cholesterol: may modestly lower total and LDL cholesterol Atherosclerosis and dyslipidaemia →
- Promoted for high blood pressure: limited evidence of a small effect
Adverse effects
Common
- Breath and body odour
- Abdominal pain, gas and nausea
- Allergic reactions
- Skin burns when raw garlic is applied to the skin
Contraindications
- Supplement doses with anticoagulants or antiplatelets without supervision
- Before surgery
- Supplement doses (more than in food) in pregnancy
Key interactions
- Warfarin and other anticoagulants
- Higher bleeding risk
- Acetylsalicylic acid and other antiplatelets
- Additive antiplatelet effect
What is monitored
- INR and bleeding signs in patients on warfarin
- Lipid profile if used for cholesterol
Pregnancy and breastfeeding
Garlic as food is fine, but amounts larger than those in food may not be safe in pregnancy.
Nursing care
- Ask every patient about herbal products and supplements and record them with the medicine list
- Ask about garlic supplements before surgery and in patients on anticoagulants
- Teach that «natural» does not mean safe and that supplements are not approved as medicines before sale
Pharmacokinetics
- Absorption
- Taken by mouth as fresh garlic, dried powder or aged extract; enteric coating protects the enzyme that makes allicin
Test yourself
Think of the answer, then tap the question to see it.
Which compound forms when garlic is crushed?
Allicin, from alliin.
What is the best-supported effect of garlic supplements?
A modest fall in total and LDL cholesterol in people with high cholesterol.
Why is a garlic supplement relevant before surgery?
It may increase bleeding risk, especially with anticoagulants or aspirin.
Connections
← Back to the class: Herbal products and dietary supplements
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Garlic: Usefulness and Safety (National Center for Complementary and Integrative Health (NCCIH), 2025).
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Representative model, for educational purposes only.