Well, yes and no. In 2014, Philadelphia became America’s largest city to remove criminal penalties for possession of less than 30 grams of the plant and up to 8 grams of hash. Arrests dropped by an estimated 10,000, saving the city millions. However, buying or purchasing marijuana does not fall under the scope of the decriminalization ordinance. Neither obviously does selling it, which is still a felony (called Possession with the Intent to Deliver).
The Philadelphia local ordinance has been allowing police to issue a civil citation to defendants instead of arresting them and charging them with Possession of a Small Amount of Marijuana. The ordinance calls for the defendant to pay a $25 fine for possession of less than 30 grams of marijuana and a $100 fine if the defendant was caught by police smoking marijuana in public. In most cases, the Philadelphia police will issue the civil citation (or simply throw the marijuana out) instead of arresting someone with a small amount of marijuana, and therefore the citation will not lead to the person having a criminal record or an arrest for drugs showing up on a criminal background check.
The ordinance does not apply to the sale of marijuana or to possession of more than 30 grams. It is also still a felony under state law to grow even one marijuana plant. Plus, possession of more than 30 grams of marijuana even for personal use may still be charged as Knowing and Intentional Possession of a Controlled Substance, which is an ungraded misdemeanor punishable by up to one year in jail for a first offense. Also, if the police believe they observed a person selling marijuana, then the police will often arrest the buyers and charge them criminally instead of issuing the ticket. This serves to document the fact that the buyers actually existed, which will often be used to bolster the prosecution’s case in the Possession with the Intent to Deliver trial against the seller. So, one still has to be careful in regards to marijuana.