text: why is marijuana illegal in the us? alcohol is a far stronger then thc and i wanted to know the background of why marijuana is illegal. there was a big anti-marijuana crusade back in the 1930s when millionaires such as hearst & dupont considered hemp to be an economic threat to their pulp mills (hemp is cheaper, more durable & saves more trees).  today, i suspect that it may be the big pharmaceutical companies that are so against marijuana. because it can be used for such a wide range of ailments & can be grown so cheaply, it's considered a threat to drug manufacturers because they would lose money.