Answer:
These claims are definitely sound due to the fact that whenever any demanded thing is sold privately or illegally, the price of that particular thing is always higher.
Hence, when the drugs are legalized , this means that anyone can purchase them from several location, hence, this will reduce the price of the drug as it will now be common and will increase the quantity demanded of the product as well because the people who once were not able to afford that drug due to being expensive, can now easily afford it.
Good Luck
Hope this clear things up.