Economic growth is dependant on productivity. Productivity is dependant on innovation and scientific advancement.
In practice the way this works is if one farmer can farm 5 acres of land. The introduction of horse drawn plows may have allowed him to farm 10 acres of land. With the development of petroleum fueled tractors allowing one farmer to farm 50+ acres of land. Growth and expansion of science and technology, boost productivity. Which in turn boost the economy.
I think this is the most important factor when talking about economical growth. Technology allows humans to do more in less time, for a cheaper price (less effort is included) and in a more sustainable way on long run. Or being more strict, the economy isn't growing at all, what happens is that the resources are being used more efficiently. If we check, people nowadays are so poor like people from past ages, with the difference we have technology now, which becomes popular within time as it is upgraded.
I think spain or portugal (perhaps both?) are known for having success with drug decriminalization.
The cost of drugs and weed can also decrease once they become less regulated. Which can de incentivize drug dealers from being in a business where their profits plummet.
The effects of drugs glamourization we will see on practice in few decades. In my opinion people should be more careful of what substances they put inside their bodies.
To develop technology and achieve scientific advancement people need to have a healthy mind, body and spirit. Drugs lead directly to the opposite way of this, what can weak or slow down improvements on this field, impacting the world negatively futurely.