Herbs, supplements and HIV

January 2005     View PDF     En español

Drug interactions

St. John’s Wort (hypericin), a popular herb used for mild depression, has possibly serious interactions with protease inhibitors and non-nucleoside reverse transcriptase inhibitors (NNRTI). St. John’s Wort is processed in the body by the same enzyme used for processing many drugs, including protease inhibitors and most NNRTIs. This enzyme is called p450, and several diet supplements and herbs have reported effects on it. Depending on how these products interact with p450, using anti-HIV drugs with them could either raise or lower the blood levels of the anti-HIV drugs. Herbs with reported effects on p450 include St. John’s Wort, garlic, ginseng, melatonin, milk thistle (silymarin), geniposide and skullcap. For more detailed information on St. John’s Wort, read NIH Study Cautions Use of St. John’s Wort with Anti-HIV drugs.

At the National Institutes of Health’s (NIH) HIV clinic, one woman who started a regimen with ritonavir (Norvir) and then started on garlic supplements developed severe nausea and vomiting, which resolved after stopping the garlic. The garlic may have increased the levels of ritonavir, and thus its side effects. A second case also reported that garlic supplements may have enhanced the side effects from using ritonavir. It is unclear, however, if garlic was increasing the risks of ritonavir-related side effects or if it was the actual cause of them. (see Herbal side effects chart) Subsequently, small single-dose studies of ritonavir and garlic do not suggest a serious herb-drug interaction, but more research is needed.

Garlic may also increase the risk of side effects associated with other anti-HIV drugs. This information, coupled with knowing that garlic has an effect on p450, suggests that until more is known people should use caution when combining high doses of garlic with anti-HIV drugs that use p450. Moreover, people using the supplement with anti-HIV drugs who experience serious stomach problems (diarrhea, nausea or vomiting) might consider stopping it to see if these symptoms lessen.

A group in Pittsburgh has shown that the common herb, milk thistle, also interacts with the p450 enzyme. It may also interact with many drugs used to treat HIV.

A Canadian group has shown that vitamin A supplements (beta-carotene and other retinoids) have an effect on the p450 enzyme. While this was based on test-tube studies, the information suggests that there might be possible vitamin-drug interactions as well. It’s then easy to start wondering if food itself may interact with drugs. There are food-drug interactions, which is why certain drugs are absorbed better when taken with or without food.

Grapefruit inhibits the p450 enzyme system and in the early days of protease inhibitors some people drank grapefruit juice together with the older version of saquinavir (Invirase), which was poorly absorbed by the body, in hopes of increasing its blood levels and effectiveness. (The newer version, called Fortovase, has corrected this problem.) However, in general, drinking grapefruit juice with protease inhibitors might increase their blood levels to dangerously high levels and increase the risk of side effects.

Not a great deal is known about food-drug interactions in general. Does this mean that people should stop eating food? Absolutely not! But the point is that we don’t know how food may cause various interactions. This underscores that supplementing with vitamins, in pill forms, could carry some risks along with its unknown benefits. The value of good nutrition for overall health is well known; the value of supplementing with vitamins is not. This doesn’t mean that people should not use vitamins, but rather it means buyers beware!

An article in The Lancet reports a number of herb-drug interactions that include the following herbs:

Betel Nut
Devil’s claw
Garlic
Ginseng
Kava
Psyllium
Shankhapushpi
St. John’s Wort
Xiao chai hu tang
Chili Pepper
Dong quai
Ginkgo
Guar gum
Papaya
Saiboku-to
Sho-saiko-to
Valerian
Yohimbine