Did you try Google Trends? You can see if people are looking for the product you're looking to sell.
You also have an option to run a Survey. Survey Monkey is probably the best. You can pay and and see the results at the end.
But most importantly, what's your differentiator? Are you offering something better than your competitor or just more of the same? And don't forget, this is a regulated market. Without FDA (or whatever agency in your place) approval you can't go too far.