Marijuana should be legal for adults. Period. There is enough scientific evidence to show the downside effects on health and on society are usually quite limited. The deleterious effects on individuals and society of continuing to criminalize marijuana use are simply not justified by any scientific evidence of 'gateway' effects or other imagined scenarios. 

Since marijuana possession is now legal, all people with records related to marijuana charges that were previously illegal should now have those records deleted permanently. Those convicted of offenses that continue to be illegal due to the amount of marijuana involved should also have their records expunged. The convictions may not occur in today's climate and it seems likely the laws will be further relaxed in the near future. 

People react differently to various potential palliatives for pain. Marijuana works as pain relief for many people who have a wide variety of conditions. With a doctor's supervision, cannabis should be one of the available potential treatments for pain and other symptoms of a number of conditions, not just a specified few under specified circumstances.