Ginger is the underground rhizome of the tropical flowering plant Zingiber officinale. The term officinale in the Latin name of a plant indicates that it was sold by apothecaries in past times and thus has a long history of medicinal use. Zingiber means horn-shaped in Sanskrit and refers to the shape of the ginger rhizome. Ginger has a sharp, sweet flavour and is used to flavour foods and drinks. The oil of ginger root contains the sesquiterpenes zingiberene and ƛ-bisabolene whilst the oleoresin contains a group of pungent phenolic compounds called gingerols and their degradation products. The gingerols are widely regarded as the components of ginger and ginger extracts that are responsible for any pharmacological actions. The gingerols are structurally related to capsaicin in chilli peppers and they bind to the same pain receptors (vanilloid receptor 1, VR1) that are abundant in the mouth and skin. Activation of VR1 receptors is responsible for the searing sensation of eating chilli peppers and also presumably for the pungency of ginger. The chemical structures of capsaicin and several gingerols may be found in Dedov et al. (2002). These same VR1 receptors may also be largely responsible for the chest pain experienced during a heart attack. Dedov et al. (2002) suggest that studies with gingerols and capsaicin may help in the development of substances that interact with and block the VR1 receptor (antagonists); this may offer a new approach to some types of pain control.
There are many historical claims for the medicinal usefulness of ginger but the main focus of interest today is its potential to help with minor stomach upsets and more particularly for the control of certain types of nausea and vomiting:
• Morning sickness in pregnancy
• Postoperative sickness
• Motion sickness
• Sickness caused by cancer chemotherapy.
It is also suggested on the basis of animal studies that gingerols may exert an anti-inflammatory and analgesic effect in conditions such as osteoarthritis by inhibiting prostaglandin and leukotriene biosynthesis.
Ernst and Pittler (2000) did a systematic review of clinical trials of the efficacy of ginger for controlling nausea and vomiting from a variety of causes. They found just one study each for seasickness, morning sickness and chemotherapy-induced nausea that met their inclusion criteria. Whilst these generally favoured ginger over placebo it would be premature to draw any firm conclusions from single studies. They identified three trials in which ginger had been used for the control of postoperative nausea and vomiting. Even though two of these studies suggested a positive benefit for ginger use, when the data from the three studies was pooled the ginger was not found to be statistically more effective than the placebo. A more recent and relatively large trial with 180 patients reported that ginger did not reduce the incidence of postoperative nausea and vomiting any more than placebo in patients after they had had gynaecological laparoscopy.
It has been proposed that ginger might exert an anti-nausea and vomiting effect in motion sickness by reducing the increase in gastric rhythmicity and the rise in antidiuretic hormone (ADH or vasopressin) that accompanies motion sickness. In a small trial, Lien et al. (2003) found that pre-treatment with 1 or 2 g of ginger reduced the nausea, the increase in gastric activity and the rise in plasma antidiuretic hormone when subjects were put in a rotating chair to induce motion sickness. Two other trials using the rotating chair as a method of inducing motion sickness have not detected any beneficial effects of ginger over the placebo. Stewart et al. (1991) found that neither 500 mg nor 1 g of ginger provided any protection against motion sickness nor did it significantly affect gastric function during motion sickness; a standard motion sickness drug did register positive effects. A study to test the efficacy of several anti-sickness drugs for the National Aeronautical and Space Administration found that three doses of ginger had no more effect than the placebo. One study, in a more naturalistic setting, tested the effects of ginger upon seasickness in 80 naval cadets during a voyage. The ginger significantly reduced the tendency to vomit and reduced cold sweats but the reduction in the symptoms of nausea and vertigo did not reach significance compared with the placebo.
Barnes (2003a) has written a short review of the effects of ginger in the treatment of morning sickness during pregnancy. She concluded that although the three controlled trials she found did give generally positive support for ginger there was not sufficient evidence to recommend the use of ginger for the control of sickness in pregnancy. She also suggested that because there was almost no data on the safety of ginger extract in pregnancy that the maximum amount used in supplements should not be much greater than that which might be used in food.
Kiuchi et al. (1992) reported that gingerols inhibit the enzyme prostaglandin synthetase which synthesises prostaglandins and probably also inhibits the enzyme arachidonate 5-lipoxygenase which is involved in the synthesis of leukotrienes. As prostaglandins and leukotrienes are key mediators of the inflammatory response, these laboratory data suggest that gingerols might have anti-inflammatory and analgesic effects. They might therefore alleviate the pain and/or swelling associated with osteoarthritis by a mechanism similar to aspirin’s.
Bliddal et al. (2000) did a randomised, double-blind, crossover trial comparing the effects of ginger extracts, ibuprofen and a placebo in 56 patients with osteoarthritis of the hip or knee. Each patient spent three weeks on each of the three treatments in random order with a one week ‘wash-out’ period between each of the three treatments. Whilst some preliminary analysis did suggest a possible beneficial effect of ginger compared with the placebo over the whole study, there was no statistically significant effect of ginger compared with the placebo, and ginger was clearly less effective than ibuprofen. The authors noted that this study did not support beneficial effects of ginger but that a longer study with more potent extracts of ginger was warranted.
Ginger has a long history of safe use as a foodstuff and there have been few adverse effects noted in trials of concentrated extracts. In high doses it may cause nausea. There is no clearly established dose and different preparations will vary greatly in the amount of gingerols that they contain. One major UK manufacturer produces 100 mg tablets of ginger extract that contain the equivalent of 12 g of ginger root with a gingerol content of 15 mg per tablet.