I am very biased against any anti-depressants because I personally suffered horrible side effects and then even worse withdrawal symptoms from both Wellbutrin XL and Paxil CR. PMS is not caused by a "drug deficency" and yes many people have low magnesium and it may help to add this to your diet. There is a magnesium forum that you can check out here at curezone.
After my first pregnancy, I had terrible PMS when I started my periods where before I never suffered from more than a little bloating and maybe some constipation. I started taking Solaray Multi-Mineral which has a fairly balanced blend of calcium, magnesium, manganese, iron, copper, selenium, phosphous, zinc, ect. This has helped me in relieving the cramping, fatigue, low back pain and general 'bitchiness'. If I am constipated, I soak in Epsom Salt baths which is magnesium sulfate and it helps to relieve that pretty well. I did a Colon Cleanse 6 months ago and I feel that helped also. It took about 2 months before I noticed improvment.
Magnesium is important to heart funtion and maintaining certain levels of the endrocrine system. It doesn't hurt to try it but I would reccommend always taking it with other balanced minerals for proper absorption instead of by itself.

Good luck! I hope this helps.

i planned to do a Liver Flush last night, not realizing i was almost due for my period. pms has gotten slightly worse for me as i've gotten older and i almost always at least have some cramps and usually a day of constipation. i took the first dose of Epsom Salt and water at 6 pm as usual, but something didn't feel right and within a 1/2 hour i already had "butt pee" (the crude yet accurate phrase from the Liver Flush Forum ), which is not normal. i didn't proceed with the rest of the flush, and the next morning my period came on, but it came on easily and i have not had any cramps the whole time.

my question is why not supplement my water with a little Epsom Salt just before my period is to start? i imagine it's like taking magnesium supplements, but it alleviated both any cramps or constipation i might've had. and it's dirt cheap.

any reason why this might not be a good idea? are Epsom Salts ok to take once a month in small doses (maybe 1/2 tsp)