I started taking it (50mg) about a 6 weeks ago for an irregular heart beat. I'm also on Vitorin and Lisinopryl (high cholesterol and high blood pressure). I'm pretty sure the IHB and blood pressure issues stemmed from too much caffene intake. I've since stopped that, but now I feel tired a lot (fall asleep almost any time I find a couch or comfortable chair), not as interested in sex (could be other reasons for that) and slow weight gain (about 5 lbs so far, but I've been working to loose weight, not gain). I plan to speak with the doctor and see if I can be taken off now that I've stopped the caffene.