Drug possession is a crime in itself, even if you don't plan to sell or make it in your own home. In Texas, drug possession is listed under the Texas Controlled Substances Act, which means if you have drugs on your person, it may mean that you've violated the law.
To be convicted for drug offenses, the prosecution needs to show that you don't have a prescription for the drug and knowingly had the drug on you. There are four classes of drugs that you can be charged for having. On top of that, if you possess marijuana, it's in a class with laws for it specifically.
If you're trying to defend yourself against drug possession charges, you can use one of several defensive options. First, you can claim you don't have enough of the drug to be able to use it. For instance, if you're accused of having marijuana in your vehicle but don't have enough to smoke, it may be difficult for the prosecution to claim you were using the drug.
If your drug is medical marijuana and you have a prescription, the prosecution will not be able to make a claim and allegations based on a charge against you. If you had lost a prescription, showing your medical prescription later to the authorities may clear you of any charges.
What's important to know about the different classes of drug charges is that your penalties and sentences could be altered. Sentences and penalties are varied in the state, and the number of past convictions, the type of drug, the amount of the drug found and possession of drug paraphernalia will affect your case.
Source: FindLaw, "Texas Drug Possession Laws," accessed Dec. 22, 2015