Possession of drugs for personal use requires the following knowledge:

?Knowledge of the presence of the controlled substance

?Knowledge that the substance is in fact a controlled substance. It is not necessary that the defendant know the chemical name or the precise chemical makeup of the substance.

Possession itself may be either actual or constructive. Actual possession means that person knowingly exercises direct physical control over the controlled substance. On the other hand, constructive possession does not require actual possession but does require that a person either knowingly or have the right to exercise control over the controlled substance, either directly or through another person. Constructive possession can be found even when the right of dominion and control over the place is shared with another.

The California criminal jury instructions, known as CALJIC define the elements that must be proved by the prosecutor in order to convict the defendant for possession of an unlawful drug. CALJIC 12.00 says in relevant part:

“In order to prove this crime, each of the following elements must be proved:

1.A person exercised control over or the right to control an amount of [a controlled substance];

2.That person knew of its presence;

3.That person knew of its nature as a controlled substance; and

4.The substance was in an amount sufficient to be used as a controlled substance."

The punishment for possession of a controlled substance is punishment in the county jail up to one year or in the state prison. A first offense may have an additional fine of at least $1000 or community service. A second or subsequent offense is punished by a fine of at least $2000 or community service.

The punishment for possession of marijuana is imprisonment in the county jail up to one year .and/or by a fine up to $500 or else imprisonment in the state prison. If the amount of marijuana is less than 28.5 grams, then it is a misdemeanor, punishable by imprisonment in the county jail up to six months, and/or a fine up to $100.

Proposition 36 is a ballot initiative that sends drug offenders to treatment programs instead of prison. Proposition 36 generally applies to those people with new convictions for drug offenses who qualify for treatment provided that they are not convicted of sale or manufacture or any non-drug crimes at the same time. Offenders are excluded if they have a prior conviction for a serious or violent felony (a "strike"), unless they have served their prison time and have been out of prison for five years with no felony convictions or misdemeanor convictions involving the threat of violence. Finally, individual offenders may "opt-out" of treatment by formally refusing it, in which case they face sentencing under pre-existing law.

Diversion is a program for first-time offenders which allow the offender to avoid having a drug conviction on their record if they complete the diversion program. The accused is required to enter a plea of guilty to the drug charge, but the accused is not sentenced. Legally, a case is not final until the defendant is sentenced. The accused must then go through a series of classes undergoing random drug testing. However, if the accused tests "dirty," the defendant is deemed to have violated the terms of the diversion. This allows the court to sentence the defendant on the original guilty plea.