The active ingredient in Imodium is available in China. If that's too much information for you, skip the rest of this post. I offer it for future reference.
Travelers from the West to China often find themselves fighting gastric distress. Whether you accidentally drank some tap water (even the locals stick strictly to bottled water) or some street food disagreed with you, it's ugly. It's happened to me two out of three trips now, so here's the remedy.Loperamide hydrochloride, the anti-diarrheal ingredient in Imodium, is sold in China in the packaging pictured above right. Click for big. This box contained six capsules and cost 5.5 yen (less than $1 US). I got complete relief in four hours - though a couple days later, the medicine wore off before the illness did, and I had to start taking it again.
You may also be offered the traditional remedy pictured above left, called Seirogan. Most Chinese households keep this around. It smells horrible and it isn't fast or effective enough for a panicked traveler short on time. Especially if, say, you're about to get on a 12-hour flight. It turns out the active ingredient in Seirogan is creosote. Hence the smell: wood smoke. According to WebMD, it's safe.