I used run a lot of training courses (2 - 5 days, perhaps 2-3 times a month) as well as conference and exhibition speaking. Once when my voice was a bit worse

I used run a lot of training courses (2 - 5 days, perhaps 2-3 times a month) as well as conference and exhibition speaking. Once when my voice was a bit worse for wear, I asked a pharmacist for suggestions and he pointed out a commercial product, but said that since the main active ingredient was liquorice extract, I might as well just buy a bag of the stuff at the local store as it would be a fraction of the price. Fortunately, I like liquorice and I have to say it's always worked for me - although you'll need to consider those nearby if you're walking the room and mitigate the liquorice with perhaps a sugar-free mint.