The links between medical cannabis laws and suicide rates is a relatively new area of research.
The CATO Institute has just released an appraisal of the latest statistics from a number of University studies in the USA.
All things being equal, it would seem that in States where there are entrenched medical cannabis laws, suicide rates in young men have dropped by 5%.
If this is the case, then it is plain to see the liberalisation of cannabis laws far outweigh the continuation of prohibition policies.
The public health benefits of  legalisation are becoming plain to see.

The CATO summary can be downloaded here: MCandSuicideRates2015

The abstract can be viewed here. (The full study is behind a pay wall)
http://ajph.aphapublications.org/doi/abs/10.2105/AJPH.2013.301612