In the past, marijuana has been used for recreational purposes. There were deaths caused due to its use, which forced the governments to ban its use. Later some of the US states have lifted the ban, but this time they created strict rules for its use so that nobody could use it wrong purposes.
There are over fifteen states in the US, where you could use marijuana for medical purposes and the state of California is the one among those states. However, it is important for you to know that you are allowed to visit a clinic of medical marijuana in Los Angeles only when you have your physician's written permission with you.