Matthew J. Ruff Criminal Law Blog on Lawyers.com

In California the law allows an individual to smoke marijuana legally only if they get a doctor's permission.  Medical Marijuana Law is somewhat complex and a lawyer should be consulted if you are arrested for possession of pot.  

 In addition, a person can purchase and furnish marijuana to others if they are a medical care giver.  For the purposes of California law a “primary caregiver” means the individual designated by the person exempted under this section who has consistently assumed responsibility for the housing, health, or safety of that person.

Although the law allows for this exception, many law enforcement officers will still arrest.  Further, federal law may make the possession illegal in some circumstances.