166 Handbook of herbs and spices
Zollman, 1999; Langmead and Rampton, 2001). Interactions between herbs and
drugs may have toxic or important pharmacological effects (Penn, 1983; D’Arcy,
1991, 1993; Ernst, 1998; Miller, 1998). Some herbal treatments may interact with
drugs used in the treatment of digestive disease, causing toxicity (Table 10.6). For
example, liquorice can enhance aldosterone-like effects of prednisolone leading to
hypokalaemia and fluid retention (Langmead and Rampton, 2001). St John’s wort
enhances the activity of cytochrome P450 enzymes thereby increasing the degradation
of drugs including cyclosporin (Ernst, 1999; Mai et al., 2000; Obach, 2000). Devil’s
claw and garlic increase prothrombin time in patients on warfarin, while tamarind
increases the bioavailability of aspirin; both effects may lead to gastrointestinal
bleeding. It has also been reported that the active principle of Capsicum annum,
capsaicin, may be mutagenic, carcinogenic and a tumour promoting agent (Nagabhushan
and Bhide 1985).
10.8 Future trends...................................................................................
The use of herbal preparations by the general population is still largely unsupported
by either efficacy or safety data from clinical trials. The future of using plant and
spice extracts as medicines for various diseases associated with the gut or generally,
lies on the careful selection and evaluation of their efficacy at low concentrations and
in combinations of different components, avoiding any adverse effects on human
health. More work needs to be done in this area including human clinical studies in
order to establish safe limits for use. Moreover, herbal preparations used for medicinal
purposes should require licensing by an independent national body in order to improve
their quality and safety and to ensure that claims of efficacy are validated by randomized
controlled trials.
On the other hand, there is a major concern nowadays for the emergence and
spread of antibiotic-resistant bacteria. This concern has widened to include all
microorganisms exposed to antimicrobial agents, including the so-called ‘natural’
compounds. However, there is relatively little information on the resistance mechanisms
Table 10.6 Herbs and spices used in gastrointestinal diseases that may cause side-effects or
interactions with drugs
Herbs/spices Side effects or interactions
Aloes Diarrhoea, abdominal cramps
Anise Nausea, vomiting
Chilli/capsaicin Cough
Devil’s claw Reduced absorption of iron
Fennel Nausea, vomiting
Garlic Potentiation leading to GI bleeding when used with warfarin
Ginseng Potentiation leading to GI bleeding when used with warfarin
Gingko Reduced absorption of iron
Ginger Reduced absorption of iron
Gentian Nausea, vomiting
Liquorice Antagonist to spironolactone, hypokalaemia with prednisolone
Parsley Nausea, vomiting
Data modified from Langmead and Rampton, (2001).