Good advise - mostly. Here is another option. Play stupid. Spark up conversation with the neighbors and tell them that you think your unit(s) must have a gas, septic, whatever leak because you smell this offensive smoke like smell coming from your basement walls you are planning on calling the gas company, electric company, polution control, whatever come over and check it out and would be willing to have them come and check out their basement too if they would like- or are they experiencing the same thing. Let them know that the reason you are wanting to "check it out" now is because you have a daughter with asthma and with the "closed window winter" season you are concerned that you will not be able to air out what ever that "smell" is during the winter and are concerned for her health.
If they are smoking MJ or whatever they may be unaware that it can "float" over into your walls and this may make them think twice. They may confess, may deny, whatever but at least they will think you are inoccently wanting the smell investigated and not trying to "report" them. If it continues then go ahead and call the "authorities" whomever and report that you have a smell that is concerning to you. You don't have to confess that you believe the neighbors are doing drugs - I am sure the authorities can fingure that out on their own. This way you won't be the "bad" guy but yet still will get results.
Best of luck with your situation
C.