Herb-Drug Interactions: Ginseng

2011

Contents

Panax ginseng C.A.Mey (Araliaceae)

Synonym(s) and related species

Many species and varieties of ginseng are used.

Panax ginseng C.A.Mey is also known as Asian ginseng. Chinese ginseng, Korean ginseng, Oriental ginseng, Renshen.

Panax quinquefolius L. is also known as American ginseng.

Other species used include: Panax notoginseng (Burkill) F.H.Chen ex C.Y.Wu & K.M.Feng known as Sanchi ginseng, Tienchi ginseng and Panax pseudo-ginseng Wall, also known as Himalayan ginseng.

It is important to note that Siberian ginseng (Eleutherococcus senticosus Maxim.) is often used and marketed as a ginseng, but it is from an entirely different plant of the Araliaceae family and possesses constituents that are chemically different. It will be covered in this monograph with distinctions made throughout.

Not to be confused with ashwagandha, which is Withania somnifera. This is sometimes referred to as Indian ginseng.

Not to be confused with Brazilian ginseng, which is Pfaffia paniculata.

Pharmacopoeias

American Ginseng (US Ph 32); American Ginseng Capsules (US Ph 32); American Ginseng Tablets (US Ph 32); Asian ginseng (US Ph 32); Asian Ginseng Tablets (US Ph 32); Eleuthero (US Ph 32); Eleutherococcus (British Ph 2009, European Ph 2008); Ginseng (Panax ginseng C.A.Mey) (British Ph 2009, European Ph, 6th ed., 2008 and Supplements 6.1, 6.2, 6.3 and 6.4). Powdered American Ginseng (US Ph 32); Powdered American Ginseng Extract (US Ph 32); Powdered Asian ginseng (US Ph 32); Powdered Asian Ginseng Extract (US Ph 32); Powdered Eluthero (US Ph 32); Powdered Eluthero Extract (The United States Ph 32).

Constituents

The actual composition of ginseng extracts used varies depending on the species used and the way the root is prepared. The main constituents are the saponin glycosides such as the ginsenosides or the panaxosides in Panax species, or the eleutherosides in Eleutherococcus senticosus, which are chemically different. Also present are volatile oils containing mainly sesquiterpenes.

Use and indications

Ginseng is used to enhance the body’s resistance to stress and to improve mental and physical performance. It has also been used for diabetes, insomnia, sexual inadequacy, for degenerative conditions associated with ageing, to improve healing and as a stimulant.

Pharmacokinetics

In vitro studies of various extracts and individual ginsenosides from Panax ginseng (Asian ginseng) and Panax quinquefolius (American ginseng) have generally found little to suggest that they interfere with the activity of cytochrome P450 isoenzymes. This also seems to be the case for Eleutherococcus senticosus (Siberian ginseng) and the eleutherosides.

The ginsenosides have been reported to inhibit CYP1A2 to some extent, and various ginsenoside metabolites have been found to exert an inhibitory effect on CYP3A4. However, the clinical relevance of these in vitro findings appears to be small, as clinical studies have found that Panax ginseng and Eleutherococcus senticosus do not affect CYP3A4 (see benzodiazepines) or CYP2D6 (see dextromethorphan), and Panax ginseng also does not affect CYP1A2 (see caffeine) or CYP2E1 (see chlorzoxazone).

Some ginsenosides have been shown to be substrates for P-glycoprotein in vitro, and may actually inhibit its activity. Whether this is clinically relevant is uncertain.

Interactions overview

Panax ginseng (Asian ginseng), Panax quinquefolius (American ginseng) and Eleutherococcus senticosus (Siberian ginseng) appear to modestly lower blood-glucose levels and may therefore potentiate the blood-glucose-lowering effects of conventional oral antidiabetics, although this was not demonstrated in one study. Panax ginseng and Panax quinquefolius may reduce the effects of warfarin. As both ginsengs also contain antiplatelet components, excessive bleeding cannot be ruled out. Panax ginseng, Panax quinquefolius and Eleutherococcus senticosus may also interfere with digoxin assays and, although the evidence is limited, the psychoactive effects of ginseng may be additive with those of MAOIs. Preliminary study suggests that Panax ginseng may increase the clearance of albendazole and alcohol, but the clinical significance of this is not clear. Panax ginseng is a constituent of some Chinese herbal medicines. For interactions relating to these products, see under bupleurum.

Ginseng + Albendazole

The interaction between Panax ginseng (Asian ginseng) and albendazole is based on experimental evidence only.

Clinical evidence

No interactions found.

Experimental evidence

Panax ginseng (Asian ginseng) 10 mg/kg given intravenously to rats, increased the intestinal clearance of intravenous albendazole sulfoxide 10 mg/kg, the active metabolite of albendazole, by about 25%. The AUC was not significantly affected.

Mechanism

Uncertain. Panax ginseng may interfere with the metabolism of albendazole.

Importance and management

The findings of this study using intravenous Panax ginseng (Asian ginseng) may not apply to oral use, as is used clinically. However, even if replicated in humans, the minor changes seen in the clearance of albendazole would be unlikely to be clinically relevant. Based on this study, no action is needed if patients taking albendazole also wish to take Panax ginseng.

Ginseng + Alcohol

Panax ginseng (Asian ginseng) increases the clearance of alcohol and lowers blood-alcohol levels.

Clinical evidence

Fourteen healthy subjects, each acting as their own control, were given alcohol (72 g/65 kg as a 25% solution) with and without a Panax ginseng (Asian ginseng) extract (3 g/65 kg) mixed in with it. They drank the alcohol or the alcohol/ginseng mixture over a 45-minute period in 7 portions, the first four at 5-minute intervals and the next three at 10-minute intervals. Measurements taken 40 minutes later showed that the presence of the ginseng lowered blood-alcohol levels by an average of about 39%. The alcohol levels of 10 subjects were lowered by 32 to 51% by the ginseng; 3 showed reductions of 14 to 18% and one showed no changes at all.

Experimental evidence

In one study in rats, oral Panax ginseng (Asian ginseng) reduced the AUC of alcohol after oral, but not after intraperitoneal, administration; however, in another study, it increased the clearance of intravenous alcohol.

Mechanism

The reasons for this interaction are uncertain, but it is suggested that Panax ginseng possibly increases the activity of the enzymes (alcohol and aldehyde dehydrogenase) that are concerned with the metabolism of the alcohol, thereby increasing the clearance of the alcohol.

Importance and management

Evidence for an interaction between Panax ginseng (Asian ginseng) and alcohol comes from a clinical study, which confirms the initial findings of some experimental studies. What the reduction in blood-alcohol levels means in practical terms is not clear but the authors of the clinical report suggest the possibility of using Panax ginseng to treat alcoholic patients and those with acute alcohol intoxication; however, this suggestion needs confirmation in further clinical studies. The available data do, however, suggest that the concurrent use of alcohol and Panax ginseng is unlikely to be detrimental.

Ginseng + Antidiabetics

In patients with diabetes taking various oral antidiabetics, Panax quinquefolius (American ginseng) and Panax ginseng (Asian ginseng) have both shown modest reductions in postprandial glucose levels after a glucose tolerance test, but Panax ginseng did not result in any improvement in diabetes control when given for 12 weeks.

Clinical evidence

In a placebo-controlled crossover study, 19 patients with well-controlled type 2 diabetes were treated with oral Panax ginseng (Asian ginseng) 2g three times daily 40 minutes before meals in addition to their usual treatment (antidiabetics and/or diet) for 12 weeks. The ginseng had no effect on glycosylated blood-glucose, which remained at about 6.5%, but it did slightly decrease the blood-glucose levels after a 75 g oral glucose tolerance test. All patients in the study were diet controlled: 5 patients received no additional treatment; 3 patients were taking a sulfonylurea; 3 patients were taking metformin; 5 patients were taking a sulfonylurea with metformin; 1 patient was taking a sulfonylurea with metformin and rosiglitazone; 1 patient was taking a sulfonylurea and rosiglitazone; and 1 patient was taking acarbose.

In earlier studies by the same research group, single dose Panax quinquefolius (American ginseng) 3 to 9 g slightly reduced the postprandial blood-glucose concentrations by about 20 to 24% in patients with type 2 diabetes when given 40 minutes before or at the same time as a 25 g oral glucose challenge. These patients were being treated with diet alone, sulfonylureas, or sulfonylureas plus metformin. When comparing the effect between those receiving antidiabetics and those not, there was no difference, suggesting no specific drug interaction.

Experimental evidence

The blood-glucose-lowering effects of Panax quinquefolius (American ginseng) and Panax ginseng (Asian ginseng) has been demonstrated in various animal models, and is not covered here because there is adequate clinical information. In an experimental study, Eleutherococcus senticosus (Siberian ginseng) also showed significant blood-glucose-lowering activity in mice.

Mechanism

Additive blood-glucose-lowering effects are theoretically possible when ginseng is given with antidiabetics. However, very limited data suggest no specific interactions with conventional antidiabetics.

Importance and management

These studies show that Panax ginseng (Asian ginseng) and Panax quinquefolius (American ginseng) might possess blood-glucose-lowering activity, but the multiple-dose study showed that this was not clinically relevant in patients with well-controlled diabetes. The available data suggest that it is very unlikely that a dramatic hypoglycaemic effect will occur in patients with diabetes.

Eleutherococcus senticosus (Siberian ginseng) may also have blood-glucose-lowering properties.

Ginseng + Benzodiazepines

Eleutherococcus senticosus (Siberian ginseng) did not alter the pharmacokmetics of alprazolam, and Panax ginseng (Asian ginseng) did not alter midazolam metabolism.

Clinical evidence

A study in 12 healthy subjects found that Eleutherococcus senticosus (Siberian ginseng), 485 mg twice daily for 15 days, did not significantly affect the pharmacokmetics of a single 2-mg dose of alprazolam given with the morning dose on day 14.

Similarly, in 12 healthy subjects, Panax ginseng (Asian ginseng), 500 mg three times daily for 28 days, did not significantly affect the metabolism of oral midazolam 8 mg. The ginseng preparation used was standardised to 5% ginsenosides. These findings were repeated in a later study using the same criteria in 12 elderly healthy subjects.

Experimental evidence

No relevant data found.

Mechanism

These studies showed that neither Eleutherococcus senticosus nor Panax ginseng had any effect on the cytochrome P450 isoenzyme CYP3A4, by which alprazolam and midazolam are metabolised.

Importance and management

These studies suggest that both Panax ginseng (Asian ginseng) and Eleutherococcus senticosus (Siberian ginseng) are unlikely to affect the metabolism of alprazolam and midazolam. Therefore no dosage adjustments would appear necessary on concurrent use.

Alprazolam and midazolam are used as probe drugs for CYP3A4 activity, and therefore these results also suggest that an interaction between Panax ginseng or Eleutherococcus senticosus and these benzodiazepines as a result of this mechanism is unlikely.

Ginseng + Caffeine

Panax ginseng (Asian ginseng) did not alter caffeine metabolism in one study. Note that both ginseng and caffeine have stimulant effects.

Clinical evidence

In a study in 12 healthy subjects Panax ginseng (Asian ginseng),

500 mg three times daily for 28 days, did not significantly affect the pharmacokmetics of caffeine 100 mg. The ginseng preparation used was standardised to 5% ginsenosides. These findings were repeated in a later study using the same criteria in 12 elderly healthy subjects.

Experimental evidence

No relevant data found.

Mechanism

These studies show that Panax ginseng does not have a clinically significant effect on the cytochrome P450 isoenzyme CYP1A2 by which caffeine is metabolised.

Importance and management

These studies suggest that Panax ginseng (Asian ginseng) is unlikely to affect the metabolism of caffeine. Therefore it would not be expected to reduce the effects or increase the adverse effects of caffeine. Nevertheless, ginseng is considered to be a stimulant, and it is possible that additive stimulant effects might occur with caffeine, although there do not appear to be many data on this. However, if both substances are given, bear the possibility of increased stimulant effects in mind.

Caffeine is used as a probe substrate for CYP1A2 activity, and therefore these results also suggest that a pharmacokinetic interaction as a result of this mechanism between Panax ginseng and other CYP1A2 substrates is unlikely.

For information on one study where the stimulant effects of a caffeine-containing herb appeared to be additive to those of Panax ginseng, see Ginseng + Herbal medicines; Guarana.

Ginseng + Carbamazepine

For mention that saiko-ka-ryukotsu-borei-to and sho-saiko-to (of which ginseng is one of a number of constituents) did not affect the pharmacokmetics of carbamazepine in animal studies, see Bupleurum + Carbamazepine.

Ginseng + Chlorzoxazone

Panax ginseng (Asian ginseng) did not alter chlorzoxazone metabolism in one study.

Clinical evidence

In a study in 12 healthy subjects, Panax ginseng (Asian ginseng) 500 mg three times daily for 28 days did not significantly affect the pharmacokmetics of chlorzoxazone 500 mg. The ginseng preparation used was standardised to 5% ginsenosides. These findings were repeated in a later study using the same criteria in 12 elderly healthy subjects.

Experimental evidence

No relevant data found.

Mechanism

These studies show that Panax ginseng does not have a clinically significant effect on the cytochrome P450 isoenzyme CYP2E1 by which chlorzoxazone is metabolised.

Importance and management

These studies suggest that Panax ginseng (Asian ginseng) is unlikely to affect the pharmacokmetics of chlorzoxazone. Chlorzoxazone is used as a probe drug for CYP2E1 activity, and therefore these results also suggest that a pharmacokinetic interaction as a result of this mechanism between Panax ginseng and other CYP2E1 substrates is unlikely.

Ginseng + Dextromethorphan

Eleutherococcus senticosus (Siberian ginseng) does not appear to affect the metabolism of dextromethorphan.

Clinical evidence

A study in 12 healthy subjects found that Eleutherococcus senticosus (Siberian ginseng), 485 mg twice daily for 14 days, did not significantly affect the metabolism of a single 30-mg dose of dextromethorphan.

Experimental evidence

No relevant data found.

Mechanism

This study shows that Eleutherococcus senticosus does not have a clinically significant effect on the cytochrome P450 isoenzyme CYP2D6 by which dextromethorphan is metabolised. Note also that Panax ginseng (Asian ginseng) had no effect on the metabolism of debrisoquine, another CYP2D6 probe substrate, in clinical pharmacokinetic interaction studies.

Importance and management

This study suggests that Eleutherococcus senticosus (Siberian ginseng) is unlikely to interact with dextromethorphan. Dextromethorphan and debrisoquine are used as probe drugs for CYP2D6 activity, and therefore these results also suggest that a pharmacokinetic interaction as a result of this mechanism between Panax ginseng (Asian ginseng) or Eleutherococcus senticosus and other CYP2D6 substrates is unlikely.

Ginseng + Digoxin

Ginseng has been shown to interfere with some methods of measuring serum digoxin, see Ginseng + Laboratory tests, below.

Ginseng + Food

No interactions found.

Ginseng + Herbal medicines; Guarana

The stimulant effects of guarana, a caffeine-containing herb, appear to be additive to those of Panax ginseng (Asian ginseng).

Clinical evidence

In a well-controlled single-dose study in healthy subjects, guarana extract 75 mg improved cognitive performance in ‘attention’ tasks and Panax ginseng (Asian ginseng) 200 mg improved ‘memory’ tasks. The combination improved both attention and memory tasks, with no clear evidence for synergistic effects, except for better performance in the increased serial sevens subtractions compared with either drug alone. In this study, the ginseng extract was standardised to 4% of ginsenosides, and the guarana extract to 11 to 13% of xanthines (caffeine and theobromine), or a maximum of about 10 mg of caffeine per dose.

Experimental evidence

Because of the quality of the clinical data available, experimental evidence has not been sought.

Mechanism

Both guarana and ginseng are used for their putative stimulative effects. In this study, they affected different tasks and, in combination, their effects were generally additive. The effect of guarana was not considered to be solely attributable to the caffeine content, since the dose of caffeine was low.

Importance and management

Caffeine-containing herbs such as guarana are often combined with ginseng for their stimulant and cognitive effects. This study provides some evidence that they do not appear to have synergistic effects, but that the combination is the sum of the different effects of the two herbs. Note that the guarana dose used in this study provided only a low dose of caffeine.

Ginseng + Laboratory tests

Panax ginseng (Asian ginseng), Panax quinquefolius (American ginseng) and Eleutherococcus senticosus (Siberian ginseng) may interfere with the results of digoxin assays.

Clinical evidence

A 74-year-old man who had been taking digoxin for many years (serum levels normally in the range 0.9 to 2.2nanograms/mL) was found, during a routine check, to have digoxin levels of 5.2nanograms/mL, but without evidence of toxicity or bradycardia or any other ECG changes. The levels remained high even when the digoxin was stopped. It turned out he had also been taking Eleutherococcus senticosus (Siberian ginseng) capsules. When the ginseng was stopped, the digoxin levels returned to the usual range, and digoxin was resumed. Later rechallenge with the ginseng caused a rise in his serum digoxin levels. No digoxin or digitoxin contamination was found in the capsules, and the authors of the report also rejected the idea that the eleutherosides (chemically related to cardiac glycosides) in ginseng might have been converted in vivo into digoxin, or that the renal elimination of digoxin might have been impaired, since the patient showed no signs of toxicity.

Experimental evidence

Panax ginseng (Asian ginseng), Panax quinquefolius (American ginseng) and Eleutherococcus senticosus (Siberian ginseng) have been found to interfere with some digoxin assays including fluorescence polarisation immunoassay (FPIA, Abbott Laboratories) and microparticle enzyme immunoassay (MEIA, Abbott Laboratories). The more specific monoclonal antibody-based digoxin immunoassay, Tina-quant (Roche), was unaffected by all the ginsengs, and the Beckman (Synchron LX system) monoclonal assay was unaffected by Panax ginseng (Asian ginseng).

Mechanism

Uncertain. One possible explanation is that the ginsengs affected the accuracy of the digoxin assays so that they gave false results.

Importance and management

The interference in the digoxin measurements described in the assays was not as high as that reported in the elderly patient and there is some doubt as to whether the herbal medicine taken by the patient was actually Eleutherococcus senticosus (Siberian ginseng). So, whether this is clinically important, and measurement of serum digoxin levels is actually affected, is uncertain. Nevertheless it may be sensible to ask about ginseng use when interpreting unexpected digoxin levels and consider using a more specific monoclonal immunoassay.

Ginseng + MAOIs

Case reports describe headache, insomnia and tremulousness, which was attributed to the concurrent use of ginseng and phenelzine.

Clinical evidence

A 64-year-old woman taking phenelzine (60 mg daily) developed headache, insomnia and tremulousness after taking Natrol High, a product containing ginseng, probably Eleutherococcus senticosus (Siberian ginseng). She had the same symptoms on another occasion after drinking a ginseng tea (type not stated), which she had used without problem before starting phenelzine. Threeyears later, while taking phenelzine 45 mg daily, she experienced the same symptoms and an increase in depression 72 hours after starting to take ginseng capsules (type not stated) and a herbal tea.

Another depressed woman taking ginseng (type not stated) and bee pollen experienced relief of her depression and became active and extremely optimistic when she started to take phenelzine 45 mg daily, but this was accompanied by insomnia, irritability, headaches and vague visual hallucinations. When the phenelzine was stopped and then re-started in the absence of the ginseng and bee pollen, her depression was not relieved.

Experimental evidence

No relevant data found.

Mechanism

Uncertain. It seems unlikely that the bee pollen had any part to play. Note that the ginsengs have stimulant effects, and adverse effects include insomnia, nervousness, hypertension and euphoria.

Importance and management

Evidence is limited to three case reports, and the general importance of these poorly documented early cases is unclear. It may be that these cases could just represent idiosyncratic reactions, and not be due to an interaction. The data are therefore too limited to suggest any particular caution. Nevertheless, consider the possibility of an interaction in case of an unexpected response to treatment with phenelzine (or potentially any MAOI) in a patient taking any type of ginseng.

Ginseng + Ofloxacin

For mention that sairei-to and sho-saiko-to (of which ginseng is one of a number of constituents) do not affect the pharmacokinetics of ofloxacin, see Bupleurum + Ofloxacin.

Ginseng + Tamoxifen and other oestrogen antagonists

Ginseng may contain oestrogenic compounds that might directly stimulate breast cancer growth and oppose the actions of competitive oestrogen receptor antagonists such as tamoxifen. However, there is some evidence that ginseng use before diagnosis might not adversely affect breast cancer survival.

Evidence, mechanism, importance and management

In one report ginseng root was listed as an example of a herbal medicine with oestrogenic activity that might directly stimulate breast cancer growth and oppose the actions of competitive oestrogen receptor antagonists such as tamoxifen, see Chinese angelica + Oestrogens or Oestrogen antagonists.

However, there is some evidence that ginseng use before diagnosis might not adversely affect breast cancer survival. In the Shanghai breast cancer study, 398 women who regularly used ginseng before diagnosis actually had better disease-free and overall survival over 5 years than 1057 women who had never used ginseng. Data on ginseng use had been obtained within 66 days of diagnosis of breast cancer. Most of the ginseng used was Panax quinquefolius (American ginseng) or white Panax ginseng (Asian ginseng), the average daily dose was 1.3 g of ginseng root, and the average cumulative duration of use was 4.3 months per year. It should be noted that ginseng users were of higher educational achievement and were more likely to have used tamoxifen (69% versus 61%), both factors that might contribute to increased survival. Although ginseng use post-diagnosis was assessed at follow-up interview, it was not possible to examine the effect of this on survival since there were no data on post-diagnosis use of ginseng in patients who had already died. While not conclusive, this study does provide some reassurance about the use of ginseng in breast cancer. However, a prospective randomised study is required to fully ascertain this.

Ginseng + Tolbutamide

For conflicting evidence that sho-saiko-to (of which ginseng is one of 7 constituents) might increase or decrease the rate of absorption of tolbutamide in animal studies, see Bupleurum + Tolbutamide.

Ginseng + Warfarin and related drugs

One pharmacological study found that Panax quinquefolius (American ginseng) modestly decreased the effect of warfarin, whereas another study found that Panax ginseng (Asian ginseng) did not alter the effect of warfarin. Two case reports describe decreased warfarin effects, one with thrombosis, attributed to the use of ginseng (probably Panax ginseng).

Clinical evidence

In a placebo-controlled study, 20 healthy subjects were given warfarin 5 mg daily for 3 days alone then again on days 15 to 17 of a 3-week course of Panax quinquefolius (American ginseng) 1 g twice daily. In the 12 subjects given ginseng, the peak INR was modestly reduced by 0.16, compared with a non-significant reduction of 0.02 in the 8 subjects given placebo. There was also a modest reduction in the AUC of warfarin. In this study, Panax quinquefolius root was ground and capsulated.

Evidence from two earlier case reports supports a reduction in warfarin effect. A man taking warfarin long term, and also diltiazem, glyceryl trinitrate and salsalate, had a fall in his INR from 3.1 to 1.5 within 2 weeks of starting to take ginseng capsules (Ginsana) three times daily. This preparation contains 100 mg of standardised concentrated ginseng (probably Panax ginseng (Asian ginseng)) in each capsule. Within 2 weeks of stopping the ginseng his INR had risen again to 3.3. Another patient taking warfarin was found to have thrombosis of a prosthetic aortic valve, with a subtherapeutic INR of 1.4. Three months prior to this episode his INR had become persistently subtherapeutic, requiring a progressive increment in his warfarin dose. It was suggested that this might have been because he had begun using a ginseng product (not identified).

In contrast, in a randomised, crossover study in 12 healthy subjects, ginseng capsules 1 g three times daily for 2 weeks did not affect either the pharmacokinetics or pharmacodynamics (INR) of a single 25-mg dose of warfarin taken on day 7. The brand of ginseng used was Golden Glow, each capsule containing an extract equivalent to 0.5 g of Panax ginseng (Asian ginseng) root.

Experimental evidence

A study in rats failed to find any evidence of an interaction between warfarin and an extract from Panax ginseng (Asian ginseng). See also Andrographis + Anticoagulants, for details of a lack of an interaction between Kan Jang, a standardised fixed combination of extracts from Andrographis paniculata and Eleutherococcus senticosus (Siberian ginseng), and warfarin.

Mechanism

It is unclear why ginseng might reduce the efficacy of warfarin, particularly as no pharmacokinetic interaction occurs. In vitro experiments have found that Panax ginseng contains antiplatelet components that inhibit platelet aggregation and thromboxane formation, although antiplatelet activity was not demonstrated in a study in healthy subjects. If an antiplatelet effect were confirmed, this might suggest the possibility of an increased risk of bleeding with the combination of ginseng and warfarin. There are a few reports of vaginal bleeding in women using ginseng preparations (unspecified) in the absence of an anticoagulant, but these are probably due to a possible hormonal effect of ginseng.

Importance and management

The available evidence suggests that ginseng might decrease the effect of warfarin. It is possible that the effect is greater with, or specific to, Panax quinquefolius (American ginseng), since this interacted in one study whereas Panax ginseng (Asian ginseng) did not. Although the ginseng dose was higher in the Panax ginseng study, the treatment duration was not as long, which may have obscured an effect. Moreover, the two case reports of decreased warfarin effects attributed to the use of ginseng were probably Panax ginseng.

Until further information becomes available it would seem prudent to be alert for decreased effects of warfarin and related drugs in patients using ginseng, particularly Panax quinquefolius. However, the possibility of an increased risk of bleeding due to the antiplatelet component of Panax ginseng cannot entirely be ruled out, although the clinical study suggests that this is unlikely.