Or is it unconnected in either direction? There may be studies on this, as I imagine those studying drug abuse are aware of the mood-changing effects of low light/sunshine levels.
They are probably also studying:
- is drug dependency affected by other physical influences which feel better after a drink or a drug hit (various other hormones, mental health syndromes and so on) ?
- is it caused by a wish to forget conditions like poverty, exclusion, repeated redundancy and unemployment, ?
- is it a hedonistic desire for the sensations of being high ?
- is it a wish to be "in with the crowd" if all your friends are taking them. ?
I would be inclined to think it a mixture of two or more of these, plus other influences. If you can move away from a depressed area and find a rewarding occupation somewhere else, or raise your self-esteem by some other route, you have a better chance of resisting the lure of instant gratification at the cost of future addiction, If no-one is selling drugs in your area at a price you can afford, your reaction to any of these would probably be alcohol or religion
Or perhaps a life of crime to fund the habit - which makes you vulnerable to exploitation and danger, which adds a different set of problems.