Part 4 of 6 in the "Chinese herbs and Western medication" series. All six are listed at the foot.
Parts 2 and 3 covered the routes. This part is organised by Western drug class, because a class is easier to match against your own medication list than a single herb.
The short version
- The Hong Kong Hospital Authority says to take particular care with drugs that have a narrow therapeutic window, such as warfarin and digoxin, so those two head the table.
- "Narrow therapeutic window" means the gap between the amount that works and the amount that causes trouble is small. Push the level up or down a little with a herb, and the consequence shows more readily than with other drugs.
- The anticoagulant warfarin: the Authority sorts its herb examples into four groups by cause — raising the blood level, antiplatelet action adding up, inhibiting metabolism, speeding metabolism. The first three may increase the risk of bleeding; the fourth may weaken the effect.
- The heart-failure medication digoxin, blood-pressure medication and blood-glucose medication: all three sit in the table below, with what you do about each.
- These are the Authority's examples, not a list where anything unlisted is safe. The same goes for the classes: a class not listed here is not thereby cleared.
- Never stop or reduce any medicine in the table on your own. Four more classes are in part 5.
First, the one thing never to do
⚠️ A safety note: TCM and Western medicine complement each other. It is not a choice between them. This whole part names Western drug classes. Whichever one you recognise, never stop on your own — do not stop, reduce or adjust any prescribed Western medication because you read this, since changes to a prescription are decided by the doctor who wrote it.
The full account is in part 1.
I. First, "narrow therapeutic window"
The Hospital Authority says to take particular care with drugs that have a narrow therapeutic window, such as warfarin and digoxin, so those two head the table.
"Narrow therapeutic window" means the gap between the amount that works and the amount that causes trouble is small. Push the level up or down a little with a herb, and the consequence shows more readily than with other drugs.
Every herb example in the table below comes from the Hong Kong Hospital Authority's lecture material; where a sentence draws on another source, the cell says so.
The table uses the numbers ②, ③ and ⑤, which are routes from parts 2 and 3: ② distribution and ③ metabolism are about how the body handles a medicine, and ⑤ additive is about two medicines' effects pushing the same way.
💡 Remember: a class is more useful than a herb name. You may not recognise 葛根, but you will recognise "blood-pressure medication" on the box.
II. Four classes, and what you do
| Drug class | Why it needs attention | What you do |
|---|---|---|
| Anticoagulant: warfarin | Narrow therapeutic window. The Hospital Authority sorts its herb examples into four groups by cause. Raise its concentration in the blood: 黄连 and 黄柏. Antiplatelet action that adds to its anticoagulant effect: 丹参 (danshen), 益母草 (motherwort), 当归 (dang gui), 黄芪 (astragalus), 党参 (codonopsis), 葛根 (kudzu root) and 姜黄 (turmeric). Inhibit its metabolism: 枸杞子 (goji berry). All three groups may strengthen its effect and increase the risk of bleeding. Speed its metabolism: 人参 (ginseng) and 西洋参 (American ginseng), which may weaken its effect and increase the risk of blood clotting inside the vessels. Set against parts 2 and 3, the four groups travel routes ② distribution, ⑤ additive, ③ metabolism slowed and ③ metabolism sped up. China Medical University's material adds that in an animal study, interaction was still observed at a two-hour gap. | Say so at the start of the consultation; whether blood-test monitoring changes is the prescribing doctor's call; never stop on your own |
| Heart-failure medication: digoxin | Narrow therapeutic window. 麻黄 (ephedra), 枳实, 枳壳 (bitter orange), 附子 (processed aconite), 川乌 and 葶苈子 contain constituents that strengthen heart-muscle contraction, adding to digoxin's action, which may worsen its side effects on the heart and lead to irregular heartbeat; 甘草 (liquorice) may cause low blood potassium, which makes digoxin's side effects on the heart more likely. | Say so at the start of the consultation; never stop on your own; if you notice an irregular heartbeat or feel unwell, seek medical attention promptly |
| Blood-pressure medication | The ephedrine in 麻黄 (ephedra) may raise heart rate and blood pressure, and taken together may cancel out the antihypertensive's effect; 葛根 (kudzu root) has a blood-pressure-lowering action of its own, strengthening the drop and easily causing a low-blood-pressure reaction; the glycyrrhizin in 甘草 (liquorice) may cause water retention, which taken together may reduce the drug's effect; 枳壳 and 枳实 can inhibit drug metabolism in the liver, and taken with felodipine may increase the risk of low blood pressure. Liquorice with the diuretic frusemide may add to the risk of low potassium and so trigger an irregular heart rhythm. | Do not change your Western medication schedule; space the herbs at least one to two hours away, and tell both sides; never stop on your own |
| Blood-glucose medication | 人参 (ginseng), 西洋参 (American ginseng), 葛根 (kudzu root), 桑叶 (mulberry leaf), 黄连 and 肉桂 (cinnamon bark) have a glucose-lowering action that adds to the medication's effect, so low blood glucose comes easily; 麻黄 (ephedra) and 甘草 (liquorice) have a glucose-raising action that cancels against it. | Tell both sides; keep taking your glucose readings as usual and bring them to your follow-up; never stop or reduce on your own |
These are the Hospital Authority's examples, not a list where anything unlisted is safe. The same goes for the classes in the table: a class not listed here is not thereby cleared.
If you take several Western medications, have a chronic condition under regular review, are pregnant or breastfeeding, are a child or an older adult, or have a liver or kidney condition, give the full medication picture at the consultation.
Never stop or reduce any medicine in the table on your own.
Four more classes are in part 5: cholesterol medication (statins, with the red yeast rice story), anti-epileptics, bronchodilators, and medicines used in surgery and anaesthesia.
A note: this section is general information only. For conditions like these, follow your doctor's diagnosis and treatment, and seek medical attention when you need it.
The words in this part
- Narrow therapeutic window (治疗窗窄) — the Hospital Authority names this class as needing particular care, and gives warfarin and digoxin as its examples. It means the gap between the amount that works and the amount that causes trouble is small.
- Anticoagulant: warfarin (华法林) — this is how the Hospital Authority labels it on its material: warfarin, 华法林, an anticoagulant. Station ② distribution in part 2 works from it as well.
- Heart-failure medication: digoxin (地高辛) — the Authority adds one line about it on the same material: digoxin strengthens heart-muscle contraction. Which is why something else that strengthens heart-muscle contraction, added on top, is additive.
- Low blood potassium (低血钾) — potassium in the blood running low. The Authority puts it in two places: liquorice may cause it, making digoxin's side effects on the heart more likely; and liquorice with the diuretic frusemide may add to the risk of it, and so trigger an irregular heart rhythm.
- Low blood glucose (低血糖) — blood glucose dropping too far. The Authority's example: a herb with a glucose-lowering action adds to glucose-lowering medication, and low blood glucose comes easily.
Frequently asked
Once I start herbs, can I lower my Western dose? Not on your own. Any reduction or stop is the prescribing doctor's decision; raise it at your next appointment. The blood-glucose row above shows why: some herbs push blood glucose lower, others push it up, and whether and how to adjust is a judgement only the doctor who sees your glucose record and your medication list can make.
My box gives a drug name, not a class. How do I match it? Photograph the box and show it at the consultation; you do not have to classify it yourself. The pharmacist at the pharmacy counter is also someone you can ask, especially about the Western side.
The other five parts
- Part 1: Can you take Chinese herbs with Western medication? The answer first, and the one thing never to do
- Part 2: How it actually happens: the four stations a medicine passes in the body
- Part 3: How far apart is far enough — and the two routes a gap does not reach
- Part 5: Red yeast rice and statins: when the supplement contains the drug, and three more classes to mention
- Part 6: What actually happens at the consultation, and fitting it into life in Malaysia
👉 If you are on Western medication and want to know how Chinese herbs should be arranged around it, you are welcome to book an online consultation with HansMed, where a practitioner registered under the T&CM Act 2016 assesses it with your medication list in view. Make sure your doctor knows about the arrangement too; safety rests on both sides having the full picture.
Sit with a licensed TCM practitioner from wherever you are.
HansMed Modern TCM
For general wellness education only — not medical advice. Consult a registered TCM practitioner for personal guidance.
Sources
- Hospital Authority, Hong Kong, Smart Patient lecture deck, 《當中藥師遇見藥劑師——認識中西藥相互作用》, PDF created 9 July 2024 — https://www.smartpatient.ha.org.hk/smart-patient-web/useful-information/sp-series/sp-series-details/%E8%97%A5-%E5%AF%86-%E8%A7%A3%E9%8E%96%E8%AC%9B%E5%BA%A7
- Institute of Integrated Chinese and Western Medicine, China Medical University, "中藥、西藥宜間隔多少時間？", page text updated 22 July 2026 — https://dhi.cmu.edu.tw/info/index.php?option=com_content&view=article&id=63&Itemid=83
