Grey Literature for Health Sciences

Google Scholar can be useful for finding grey literature, but this 2015 study suggests that it shouldn't be the only source searched: 

Haddaway NR, Collins AM, Coughlin D, Kirk S (2015) The Role of Google Scholar in evidence reviews and its applicability to grey literature searching. PLoS ONE 10(9). doi:10.1371/journal.pone.0138237

Note that you'll need to take a different approach to building search strategies in Google and Google Scholar than in many other databases:

• Truncation/wildcard searching is not supported
• Google Scholar has a 256 character limit for searches; Google limits to 150 words
• Google and Google Scholar show only the first 1000 results
• Nesting terms in parentheses - eg, (science OR technology) AND (british columbia OR alberta) - does not work as it does in other databases

For more details, see:

Bramer WM, Giustini D, Kramer BM, Anderson P (2013). The comparative recall of Google Scholar versus PubMed in identical searches for biomedical systematic reviews: a review of searches used in systematic reviews. Systematic Reviews 2(115). http://doi.org/10.1186/2046-4053-2-115

Advanced search operators give you more control over what results Google returns:                           

For an excellent resource on searching with Google see the Google Advanced Power Searching page.