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:
Urologically yours,
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
