There wouldn't be a dramatic increase in the use of hard drugs because all of the stigmas surrounding them would still remain. There would probably be a slight increase in the use of soft drugs initially, but should stabilize after a while.

There would be a significant decrease in the amount of fatal overdoses, because the drugs would now be regulated and standardized. If drug paraphernalia like hypodermic syringes became readily available, there would be significantly fewer cases of diseases like HIV and hepatitis C being spread by the sharing of needles.

This would also have a tremendous impact on street gangs and crime syndicates, as most of their money comes from illegal drugs sold on the black market. It would also completely wipe out cartels and narcoterrorist.

There wouldn't be an increase in the price of drugs either, there would actually be a decrease in the price even after taxes, because currently the price of illegal street drugs are extremely inflated, cocaine for example has an inflation rate of around 4000%.

And it would be a great way to generate money through taxes and get rid of groups like the DEA.

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Legalization, regulation, and taxation
is the only solution to the drug problem.