Herb-Drug Interactions: Lycium
Lycium barbarum L. (Solanaceae)
Synonym(s) and related species
Chinese wolfberry, Goji berries, Matrimony vine, Wolfberry. Lycium chinense.
Constituents
Lycium fruit contains carotenoids such as betacarotene and zeaxanthin, beta-sitosterol, linoleic acid, betaine and various polysaccharides, vitamins and amino acids. The root bark contains beta-sitosterol and betaine among other constituents.
Use and indications
Lycium (dried berries or root bark) has been used to treat diabetes, ophthalmic disorders, hypertension and erectile dysfunction, and is thought to possess anti-inflammatory, antioxidant and anticancer properties. The dried berries are also used as a foodstuff.
Pharmacokinetics
In vitro studies suggest that lycium may be a weak inhibitor of the cytochrome P450 isoenzyme CYP2C9, although this is considered insufficient to cause a drug interaction, see warfarin8.
Interactions overview
Lycium has antidiabetic effects, which may be additive to conventional antidiabetics, although evidence for this is largely experimental. A case report suggests that lycium may enhance the effects of warfarin, but this does not appear to be as a result of inhibiting CYP2C9, as has been suggested by some sources.
Lycium + Antidiabetics
The interaction between lycium and antidiabetics is based on experimental evidence only.
Clinical evidence
No interactions found.
Experimental evidence
In an experimental study in rats with streptozotocin-induced type 2 diabetes, Lycium barbarum polysaccharide (extracted from the fruit of lycium) decreased insulin resistance, and reduced fasting insulin and postprandial glucose levels. In another study, a fruit extract of Lycium barbarum 10 mg/kg twice daily for 10 days significantly reduced blood-glucose levels in diabetic rabbits but did not reduce blood-glucose levels in healthy mice.
Mechanism
Lycium appears to improve glucose transport and increase insulin signalling thereby reducing blood-glucose levels. In theory, these effects may be additive with conventional antidiabetics.
Importance and management
The evidence is limited and purely experimental but what there is suggests that lycium may have antidiabetic properties. This is supported by the traditional use of lycium, in diabetes. Therefore, there is a theoretical possibility that lycium may enhance the blood-glucose-lowering effects of conventional antidiabetics. However, until more is known, it would be unwise to advise anything other than general caution.
Lycium + Food
No interactions found. Note that lycium berries are used as a foodstuff.
Lycium + Herbal medicines
No interactions found.
Lycium + Warfarin
A case report suggests that lycium may enhance the effects of warfarin.
Clinical evidence
A 61-year-old Chinese woman stabilised on warfarin (INR normally 2 to 3) had an unexpected rise in her INR to 4.1, which was identified during a routine monthly check. No bleeding was seen. She was also taking atenolol, benazepril, digoxin and fluvastatin. It was found that 4 days before visiting the clinic she had started to take one glass (about 170 mL) 3 or 4 times daily of a Chinese herbal tea made from the fruits of lycium to treat blurred vision caused by a sore eye. When the herbal treatment was stopped, her INRs rapidly returned to normal.
Experimental evidence
See under Mechanism, below.
Mechanism
Warfarin is metabolised by a number of isoenzymes, the most important being CYP2C9. Inhibition of this isoenzyme may therefore lead to increased warfarin levels and effects. The authors also carried out an in vitro study and concluded that, although lycium is a weak inhibitor of the cytochrome P450 isoenzyme CYP2C9, this is insufficient to cause an interaction. However, they note that other mechanisms cannot be ruled out.
Importance and management
Although the authors suggest avoiding the concurrent use of lycium and warfarin, because of the many other factors influencing anticoagulant control, it is not possible to reliably ascribe a change in INR specifically to a drug interaction in a single case report without other supporting evidence. It may be better to advise patients to discuss the use of any herbal products that they wish to try, and to increase monitoring if this is thought advisable. Cases of uneventful use should be reported, as they are as useful as possible cases of adverse effects. It should be noted that lycium berries are also used as an ingredient in Chinese foods.
