Ingesting a tapeworm is dangerous. Repeat after us.
Tapeworms are intestinal parasites, and when you consume one it will literally sink its hooks into you -- after you swallow it (and you can purchase them in capsule form), it latches its head into your intestinal wall and when you eat, your new parasitic friend absorbs some of the nutrients before your body does. Yes, you will lose weight, but you will gain a tapeworm that could grow as large as 30 feet (9 meters), which will cause pain and an upset stomach -- and may even kill you.
To rid yourself of the parasite you'll need to take prescribed anti-worm medication to paralyze and starve the worm, which is then passed in your stool.