Possession of Controlled Substance
Possession charges are strict liability crimes, meaning that the State need not prove you knew what you possessed. Simply possessing the item, even unwittingly, is enough to convict. These charges are rife with Fourth Amendment (search and seizure) issues. Constitutional violations occur frequently; you will need a lawyer to curtail any abuse of power.
Possession of Marijuana
Although marijuana is legal to consume in Washington State, possessing certain amounts is still illegal. The limits are 1 oz of leafy marijuana, 16 oz of edible solid marijuana, 72 oz of edible liquid marijuana, and 7 grams of marijuana concentrate. Having more than 1 oz but under 40 grams (1.4 oz) is a misdemeanor while over 40 grams is a felony.
Use of Drug Paraphernalia
One can be charged simply for touching an object related to drugs. These objects, depending on intended use, can include things like scales, bowls, spoons, bongs, and roach clips, among others.