cell anaemia. Garlic can alter blood coagulability by decreas-
ing platelet aggregation and increasing fibrinolysis.
Adverse effects
The adverse effects of garlic use involve gastro-intestinal
symptoms including halitosis, dyspepsia, flatulence and
heartburn. Other reported adverse effects include headache,
haematoma and contact dermatitis.
Drug interactions
Garlic inhibits many drug-metabolizing (CYP450) enzymes in
vitro, but induces CYP450s when administered chronically in
vivo (reminiscent of many anticonvulsant drugs – Chapter 22 –
as well as ethanol). Clinical studies using probe-drug cocktails
have shown that garlic has no significant effect on the activity
of CYP1A2 (caffeine), CYP2D6 (debrisoquine,dextromethor-
phan) and CYP3A4 (alprazolam,midazolam). Clinical studies
suggest that garlic significantly decreases the bioavailability of
saquinavirandritonavir. These HIV protease inhibitors are not
only metabolized by CYP3A4, but are also substrates for P-gly-
coprotein. The clinical importance of these interactions is uncer-
tain, but potentially appreciable.
GINSENG
There are several types of ginseng (Siberian, Asian, American
and Japanese), the most common type used in herbal prepara-
tions being the Asian variety (Panax ginseng). In humans,
ginseng has been suggested to be a sedative-hypnotic, an
aphrodisiac, an antidepressant and a diuretic, and therapeutic
benefits have been claimed for many indications (see below).
Its pharmacologic properties include actions as a phytoestro-
gen, suggesting that its use, as with soy supplementation,
could be disadvantageous in women with oestrogen-sensitive
cancers (e.g. breast or endometrium). The active component
of ginseng, ginsenoside, inhibits cAMP phosphodiesterase
and monamine oxidase. These properties may partly explain
purported central nervous system (CNS) stimulant actions
of ginseng (though not sedative/hypnotic effects), potential
modulation of the immune system and increase of glycogen
storage. However, possible efficacy of ginseng in improving
physical or psychomotor performance, cognitive function,
immune function, diabetes mellitus and herpes simplex type 2
infections is not established beyond reasonable doubt.Adverse effects
The adverse effects of ginseng are primarily CNS effects –
agitation, irritability, insomnia and headache. Others noted
include hypertension and mastalgia.Drug interactions
In vitro evidence suggests that ginseng extracts inhibit CYP3A4
in human hepatocytes. These in vitro data are consistent with
study data during an 18-day course of ginseng where it signifi-
cantly increased the peak plasma concentration of nifedipine, a
CYP3A4 substrate, in healthy volunteers. As with other herbs
(e.g. echinacea), substantial variability in ginsenosidecontent
has been reported among commercially available ginseng
preparations, indicating that clinically significant effects on the
pharmacokinetics of drugs that are metabolized by CYP3A4
could be highly variable between batches.98 ALTERNATIVE MEDICINES:HERBALS AND NUTRACEUTICALS
Table 17.1:Most commonly used herbal products based on dollar salesProduct Plant Intended condition to Annual sales in
be used for USA ($ millions)
Garlic Allium sativum Hyperlipidaemia– 34.5
hypercholesterolaemia
Ginkgo Ginkgo biloba Dementia and claudication 33.0
Echinacea Echinacea purpurea Prevention of common cold 32.5
Soy Glycine max Symptoms of menopause 28.0
Saw palmetto Serenoa repens Prostatic hypertrophy 23.0
Ginseng Panax ginseng Fatigue 22.0
St John’s wort Hypericum perforatum Depression (mild) 15.0
Black cohosh Actaea racemosa Menopausal symptoms 12.3
Cranberry Vaccinia macrocarpon Cystitis and UTI 12.0
Valerian Valeriana officinalis Stress and sleeplessness 8.0
Milk thistle Silybum marianum Hepatitis and cirrhosis 7.5
Evening primrose Oenothera biennis Premenstrual symptoms 6.0
Bilberry Vaccinia myrtillus Diabetic retinopathy 3.5
Grape seed Vitis vinifera Allergic rhinitis 3
UTI: urinary tract infection