As with everything in life there are no quick fixes.
Smoking or drinking will only make it worse.
Try and think of better or different ways of dealing with "situations" that lead to stress. Remember there is nothing wrong with stress in moderation. If you are not stressed every to a certain extent then you are probably not going anywhere with your life or have won the lottery. The highest achievers in life are confronted with high levels of stress on a daily basis. You just need to figure out ways of dealing with it.
I am stressed at work all the time but a lot of it has to do with me procrastinating and being extremely untidy, so I never organised and my turnover of work is not as good as it should be ---> stress = vicious circle. My way of *alleviating* stress therefore is to f*****g organise myself better!
In general, as someone as already mentioned, a B-Vitamin complex is recommended.
Also, meditation is good.
However, the biggest stress buster is EXERCISE.
A healthy body = healthy mind ---> means you can cope with stress better.
Etc etc.