Theft of anything can be charged under whatever the appropriate theft offense is - under $400 in value, it's petty theft, over $400, it's grand theft. If they think you entered a building with the intent to steal, it can be burglary (second degree if it's a commercial building, first degree if it's a residence).
Then there's whatever drug charges are appropriate - anything from possession of a prescription drug without a prescription up to possession of a controlled substance, depending on the type of drug.
If they think you took enough so that you could resell, there's the possibility of possession with intent to sell.
The specifics of the case will matter. If the police contact you, do NOT make any statement without consulting with an attorney. Saying anything in this case can only hurt you. That applies to talking with anyone. No facebook, myspace or twitter posts about this. No texts messages, IM or emails. No phone calls, etc. I'd stay off the internet, as a computer search by police can uncover what you've googled. I'm not trying to put the fear of God in you - it's just that things can quickly go from bad to worse in this situation. It's time for a lawyer if you're being accused of theft.
It is a theft crime and a drug possession crime. The outcome depends on the specifics of the case, the drug and how much was stolen, the extent and nature of your criminal record if you have one, the jurisdiction, the judge, and the skill of your attorney.