Time for the chemist to put in $0.03 worth...
Tina is methamphetamine hydrochloride. Also known as crystal (more on that later). In the drug circles, crystal methamphetamine became know as "cris", then "christina,", then shortened to "tina" so that only those who understood the code would know what they were talking about.
Methamphetamine is still a pharmaceutical drug. If you have it prescribed by a doctor, and get it from a pharmacist, that's one thing. The street drug is a different story entirely. Even if you got well-manufactured, well-refined meth, long-term use is really hell on your body. The stuff you get from a friend of a friend of a friend has no quality controls. You don't have a clue exactly what they have put in it.
Almost all drugs are made with some pretty nasty chemicals, but the manufacturing and refining processes ensure that they are (at least moderately) safe to take. With the law cracking down on illicit manufacturers, these "basement factories" use substitute chemicals and shortcut processes. If they are lax about extraction procedures, or don't completely dry a product before the next step, or whatever reason, you can end up with traces in there that you really really do not want to put into your body. Add to that the fact that most street drugs are "cut", or diluted, and the dangers are compounded. Dealers really don't care what they use to cut drugs. For those who don't know, cutting involves taking (for instance) 100 grams of a drug, keeping a little (5 or 10 grams or so) for himself, and making up the difference by adding something else to make up the difference before selling it as 100 grams. (Like a bartender who waters down the liquor to make more profit). If you are extremely lucky, your dealer uses powdered sugar to cut. It is more likely that he uses whatever he can find.
Back to the crystal terminology. Many drugs, in their pure form, are not water soluble, so are of little use. React those drugs with certain kinds of acid, and you have a soluble salt of the drug, which is very useful (look at the chemical name for almost any over-the-counter drug, and it will have "hydrochloride", or "citrate" or "bromide" or something similar after the name of the active ingredient.) Benadryl, for example, is "diphenhydramine hydrochloride" or just "diphenhydramine HCl." Pure methamphetamine is a kind of gooey, oily liquid. Treat it with hydrochloric acid, and voila, it turns into a water-soluble, crystalline solid. The base materials used by street drug manufacturers are also in salt form. The process involves using lye to convert to pure form, several other chemicals to do a few substitution and addition reactions, extracting the product with a solvent (highly explosive ether works best), evaporating off the solvent, then treating the product with HCl again to get the final result. If any of these ingredients is not COMPLETELY purified out, then you get to consume them with your drug. "MMMmmmm, yummy, a little additional paint thinner in my lungs because the drug factory didn't want to use ether!"
Whether you eat it, snort it, inject it, or smoke it, you are playing russian roulette. Your luck will eventually run out and you'll get the chamber with a round in it.