Is there any difference according to Jewish law between a person who uses alcohol to get happy, for example, at a wedding, and a person who uses marijuana (or cigarettes) for the same purpose?
Yes, there is a great difference. According to halachah (Jewish practical law) it has already been determined by the great sage Rabbi Moshe Feinstein, of blessed memory, that it is prohibited for Jewish people to use marijuana because by doing so he transgresses the positive commandment of “You shall be holy” (Leviticus 19-2) (Igros Moshe, Yoreh Deyah 3 – 35).
But this is not the case in regard to drinking alcohol at the time of a simcha (festive occasion) when one’s intent is to use it as a medium to express his happiness (obviously, this is not referring to excessive drinking which itself would be a transgression of “You shall be holy”); where we do not find that one transgresses the [aforementioned] positive commandment by drinking alcohol.
In regard to cigarettes, most all of the present-day poskim (Halachic Rabbinate) are of the opinion that it is prohibited based upon the Torah restriction: “And you shall carefully guard your souls [health]”.