I recall reading a forum where humans with SM dismissed this supplement and some others as not being effective for SM (with one pointing out that if something so simple could effectively help SM pain wouldn't all the people with SM be using it? And wouldn't someone more mainstream be selling it? As the profits would be vast...!). Several had bought many such things with no result and not one posting as far as I recall, had had any improvement.
I have seen some discussions of Nerve Eight on various SM dog lists over the past 7 years, so it has been floating around for a while; and FWIW no one whose opinion I would trust has had any improvement though some at times have said they think they have seen improvement -- maybe someone here has had a better result! The problem is that SM tends to ebb and flow in many dogs anyway. A lot of the dogs that had supposed improvements were shortly back to usual SM behaviours or worsened over time so I'd find it hard to think it does much if anything.
There are a lot of these kinds of things out there, often fairly costly, where people take advantage of those desperate to find something that will help a serious illness.
I know this particular mix clearly states ingredients etc -- seems more reliable at least in its contents and also is not that expensive. It probably cannot hurt (though really it is only advertised as something to help with sleep and calm nerves) but check with your vet/neurologist about any possible clashes with existing medications if you want to use it
. Or work with a holistic vet perhaps?
There's a book called The Spam Kings that outlines how much some people make -- mind boggling amounts -- off herbal remedies advertised on websites and via spam email. Mostly they buy the herbs for practically nothing in the far east -- no verification of what is in these things -- and then sell at about 20-50 times what they pay for it. So it should be an area of caution for anyone making purchases.
The one complementary health approach that does seem to help some dogs is acupuncture (several neurologists advocate it as a possible help for some dogs). However be sure the vet acupuncturist knows about SM and is not sticking needles into the syrinx areas.