Is it true that marijuana can cause gynecomastia?

Yes and More. Gynecomastia comes from the greek meaning "gyne" meaning woman and  "mastos"  meaning breasts.  it refers to abnormal development of large mammary glands in males. Although there may be many “causes”, most cases are idiopathic (no specific cause). The use of certain medications, drugs, organ dysfunction (kidney or liver), hormonal imbalances etc. May also be causative.
Doubtful. Studies implicating marijuana as an etiology for gynecomastia are lacking. However if "the munchies" lead to heavy calorie eating then the breasts like everywhere else will get fat.
No one knows. While there has been numerous reports in the past that marijuana causes gynecomastia, none have been definitive and no one has proven the link. There has been speculation about how the association may have been made but my research into the topic has not produced one paper proving a direct cause and effect relationship.
Unknown. There is no scientific evidence of gynecomastia from marijuana, however there are other causes of gynecomastia which include decreased levels of testosterone and certain medications.