Chances are that your son is addicted to pot and will use it again. Unfortunately, sometimes pot is laced with other things like LSD,
meth, cocaine, etc. There is no saying whether he will crave the meth again (which is a highly addictive substance). Since he used it for so long, it is possible. If he has been clean for a while now, he should be safe from the toxic effects of the laced pot. However he will need long term help for dealing with the addiction he certainly has. I suggest you check the NIH
drug addiction website for resources that may help your son. The address is drugabuse.gov. Good luck.