How safe is neem oil? As it turns out, the use of neem oil is very safe, within certain parameters.
Is neem oil safe to use? Does neem have side effects?
Neem toxicity, or neem safety to word it positively, is a fairly simple issue. It can be summed up in a few points (and those three points are also in the footer on every page on my site):
Neem use is safe, provided you...
Let me repeat the last point: never give neem in any form to children with fever or viral illnesses. Neem contains Aspirin like substances and like Aspirin it can lead to Reye syndrome. (More info about children ingesting neem oil.)
Is neem oil spray safe
And if you are, or hope you soon will be, pregnant, you may also want to know how and why neem may harm you or your child. So let's look at the details.
Several small studies into neem side effects (sources) showed different results.
Some studies suggest that neem should be used with caution. Several neem extracts did show negative side effects when fed to laboratory rats in daily high doses over an extended period of time. (I have always cautioned against ingesting purified neem extracts.)
In other studies there were no side effects from neem products (including neem oil) at all, even when using large amounts, and over several generations. (Note: the studies used laboratory rats, not people...)
But neem bark and neem leaf may also make conception less likely when you take them internally. (Actually, the research used large doses of concentrated extracts, not everyday amounts of leaf or bark). Neem leaf or bark extracts stimulate the immune system, and the increased immune system activity is thought to be responsible for the contraceptive and even abortive effect of neem oil.
(More on this page: Neem And Birth Control/Neem Oil As A Contraceptive)
In short, even if there is no hard data, why take chances? Don't take neem if pregnant or trying to conceive.
(You can still use neem soap, neem shampoo, lotions, etc. and of course you can still spray it in the garden. And yes, of course you can eat the sprayed produce, too. That's not like ingesting capsules of the stuff. Just don't drink the spray...)
This is a common concern of pet owners. Especially cats, which forever clean themselves, ingest whatever you spray them with.
Some studies on laboratory rats did show negative neem side effects (again mostly related to reproduction) when neem seed oil was taken internally. Those rats were fed considerable amounts of neem oil on a daily basis. The neem side effects were reversible, meaning they disappeared when the animals stopped taking neem.
The EPA (US Environmental Protection Agency) says neem is Generally Recognized As Safe (GRAS) for use in food products. They even exempted their typical requirement for maximum pesticide residues on agricultural products.
If there are no restrictions regarding maximum allowable residues for farmers, then you also don't have to worry about residues from your neem spray in your vegetable garden. Yes, neem spray is safe. A heck of a lot safer than all the other sprays you ingest with conventionally grown produce!
There is no data or experiences that indicate any negative side effects from using fresh or dried neem leaves (unless you are pregnant/trying to conceive). But any medicinal herb should be ingested with caution. Also, please do take note of the warnings on that page regarding neem extracts. Neem leaf is not the same as leaf extract.
Apply common sense, only take neem leaf in moderation, and start with little when trying it for the first time.
For those who want to dig deeper and read all the scientific details of the individual studies, the sources are below. You can find them and more by going to the National Library of Medicine of the National Institutes of Health. Just enter "neem" (plus additional keywords) in the search box and go for it.
Trans R Soc Trop Med Hyg. 2005 Oct;99(10):769-74. Phase I safety study of Praneem polyherbal vaginal tablet use among HIV-uninfected women in Pune, India.
Ecotoxicol Environ Saf. 2004 Nov;59(3):332-9. Biochemical effects of vepacide (from Azadirachta indica) on Wistar rats during subchronic exposure.
J Ethnopharmacol. 2004 Sep;94(1):25-41. Safety evaluation of neem (Azadirachta indica) derived pesticides.
Chembiochem. 2004 Apr 2;5(4):408-21. Neem--an omnipotent plant: a retrospection.
J Basic Clin Physiol Pharmacol. 2003;14(4):387-95. Azadirachta indica adversely affects sperm parameters and fructose levels in vas deferens fluid of albino rats.
Life Sci. 2002 Nov 1;71(24):2845-65. Gastroprotective effect of Neem (Azadirachta indica) bark extract: possible involvement of H(+)-K(+)-ATPase inhibition and scavenging of hydroxyl radical.
Food Chem Toxicol. 2001 May;39(5):477-83. Azadirachtin, a neem biopesticide: subchronic toxicity assessment in rats.
Pharmacol Res. 2000 Apr;41(4):419-22. How safe is neem extract with respect to thyroid function in male mice?
Immunol Cell Biol. 1997 Apr;75(2):190-2. Plant immunomodulators for termination of unwanted pregnancy and for contraception and reproductive health.