I don't know that I was massively toxic the first time I cleansed, but I certainly wasn't non-toxic. I was 23, drinking a few nights a week, smoking about a pack a day on and off for three years, but probably for a total combined time of under two years. I ate fairly healthily, with no meat in my diet and only a little dairy. I didn't find that the detox symptoms were too bad, honestly, so I think it's a good idea, though your situation may be entirely different from my own.