I've been taking Gaia Herbs Rhodiola for about a month now. The first time I took 1 pill, I became extremely anxious and irritable for about 3 hours. It was so bad, I was never going to take any again, but near the end of this, I experienced a positive/energetic mood, and the next day I started on a smaller dosage and worked up. For about a week, I had great bursts of energy and an excellent mood. I think all this is due to the fact that Rhodiola is supposed to boost the passage of serotonin to the brain, and as with other serotonin-enhancers, such as SAM-E, there is a very fine line for me, as a little makes me feel good, but too much gives me anxiety. I had a crash about a week ago, though, and since then, I haven't noticed as much effect from the Rhodiola. My tolerance certainly increased, as I am now up to 2 pills/day with much less impressive results. I still think the Rhodiola is helping, though.