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Juniper berry toxicity.

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Juniper berries aren't that irritating to the kidneys.

I've taught for years that you can't use loads of juniper berries, because they irritate the kidneys. I haven't muttered that caution with juniper for the last few years, though, because I remembered a post about it on a list for herbalists. This one:

I think the rumors of Juniperus spp (juniper) causing kidney problems are greatly exaggerated and based on an even worse insult than the Melissa studies being extrapolated to humans. Read Tisserand's discussion of it in Essential Oil Safety. The studies suggesting renal problems actually used Juniperus sabina (savin). Look at the existing rat study (yes, they're rats) in which they practically drowned the poor buggers in Juniperus communis essential oil [link below] and guess what -- no renal damage whatsoever. Anyhow, I think it is absolutely indicated in renal infections as a combination inflammation modulator and antimicrobial, and I think it's diuretic effects wouldn't somehow be so powerful as to damage the kidneys. But I could be wrong.
That being said, I've never had a patient with pyelonephritis, so I don't actually know from personal experience what would happen. But I would include Juniperus tincture in their herbal formula, in reasonable doses.

Urologically yours,
Eric Yarnell, ND, RH(AHG)
Seattle, WA"

So there you have it. All the fuss is because savine is a juniper, too. It's toxic, as is its oil:

"Savin is emmenagogue, diuretic, diaphoretic, and anthelmintic. In large doses it will produce gastro-enteritis. Care must be taken in its administration, as it has, in several instances, produced fatal results. It should never be given when there is any general or local inflammation present, and it should never be used during pregnancy,"
(King's American Dispensatory)

"Oil of savine is a powerful irritant to the mucous tissues, and powerfully deranges the nervous system. It may induce gastro-intestinal inflammation, vesical tenesmus and strangury, congestion of the pelvic organs, fever, mental excitation and intoxication, coma, and death."
(King's American Dispensatory)

And "normal" juniper oil (Juniperus communis) isn't toxic, even in high doses, in rats. Note, a juniper tincture contains almost the same constituents as oil of juniper:

"The nephrotoxicity of juniper oil ... was evaluated in ... rats after oral administration. Two ... slightly different oil batches were tested for 28 days with 100, 333 or 1000 mg ... resp. 100, 300 or 900 mg ... juniper oil/kg. Additionally terpinene-4-ol ... was tested in a dosage of 400 mg/kg. Neither of the tested substances induced changes in function or morphology of the kidneys at the tested doses, and they were revealed to be nontoxic."
Schilcher H, Leuschner F., The potential nephrotoxic effects of essential juniper oil., Arzneimittelforschung. 1997 Jul;47(7):855-8.

Related entries: Picking juniper berries - Using juniper berries - Juniper salmon