I've noticed lately that growers are using more Neem Oil, recommending it to everyone, and dousing everything all the time with Neem believing it completely safe because it's approved for organic use.
While neem oil has a long history of use, is relatively safer then many other pesticides, and has a low toxicity for most adult humans, it has dangers and should be used carefully. Neem oil poisoning is rare but some people are highly allergic to it. And of course some people use way, way too much.
Here's a report of Neem poisoning:
Neem oil has widespread use in Indian subcontinent due to its many bioactive properties. Azadirachtin, an active ingredient, is implicated in causing the effects seen in neem oil poisoning. Neem oil poisoning is rare in adults. This report highlights the toxicity associated with neem oil poisoning in an elderly male. The patient presented with vomiting, seizures, metabolic acidosis, and toxic encephalopathy. The patient recovered completely with symptomatic treatment.
and link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3841499/
Encephalopathy is swelling of the brain, possibly fatal. I read of another case where a 35 year old woman consumed 125 ml neem oil for 5 days. Her brain swelled so much she lost her vision. It took a month of treatment to get it back.
There's been widespread cases of a phenomenon called 'scromiting' where long time cannabis users vomit and have seizures after smoking cannabis. There's a thread about it here at IC. The symptoms sound like Neem poisoning. I'll add that it's quite rare but it's been reported widely enough to get press coverage in Colorado.
Neem is is especially dangerous to babies and children. In a study performed in 1982 it was found that neem ingested by children or infants causes swelling of the brain, damage to the liver and other organs and can be potentially fatal. While not usually the consumers of cannabis I'd be very cautious if I was using the stuff around kids.
It's also a contraceptive and causes miscarriages. Pregnant women should never be around the stuff, and it's so ubiquitous in dispensary herb if you're pregnant or looking to get pregnant you shouldn't smoke or ingest it unless they test for it.
A lot of the traditional uses of Neem are topical, brushing your teeth and spitting it out, treating your skin and hair, or as a soap. When it's ingested it's small amounts for a short period of time to cure a disease. I noticed it's only fatal to insects if they ingest the leaves containing the neem. If they're just contacting it they're fine.
I wouldn't recommend smoking buds sprayed with Neem oil for any length of time, or at all if you're allergic. I think people have problems with Neem in large quantities when it saturates their system. There hasn't been testing on long or short term effects of smoking neem oil.
I'm not advocating never using Neem Oil. Like other pesticides I'd limit it's use to a couple of weeks during Veg or maybe very early flowering before the plants have developed white hair clusters. One nice thing about Neem is that it's not a carcinogen like a lot of other pesticides.
Personally I don't like the stuff. Dislike the smell, it makes me slightly nauseous. Wouldn't ever ingest the stuff and wouldn't want it on my skin because of the smell. Hope I never have to use it on my plants..