Is it effective to use over-the-counter medicines for yeast infections?

Mostly: Yes in over 70% of cases. The trick to using an otc is to be certain the infection is yeast, as there are other causes of vaginitis. I suggest women who had diagnosed yeast infections and can recognize them can always try on otc. Women who have never had a clinically diagnosed infection would do better seeing a provider first to be sure you're treating the right problem.