International Students and Cannabis Use
As international students, Marijuana (cannabis) use, even in California, is considered an illegal activity by U.S. immigration.
California State Law vs. Federal Law
California State law (Proposition 64) allows the legal sale of marijuana to people 21 and over as of January 1, 2018. This State law decriminalizes marijuana. However, Federal Law still prohibits the use or possession of marijuana.
Federal laws are established at the national level, and Federal laws override State laws. As an international student, you are subject to FEDERAL law.
When you enter the U.S., your social media accounts, texts, and email are all subject to search. Evidence of marijuana use (such as photos or texts to friends about buying or using) can be reason enough for agents to refuse entry. Use extreme caution when joking about drug use or illegal activity on your social media accounts, texts, or phone.
Again, the California State law does not change this Federal policy. Your American friends might not know that you are subject to Federal law and encourage you to use marijuana. However, you are responsible to understand the laws that are apply to you. Do not use marijuana in the U.S.