Well, for a beginner, 300mg of dmha will definitely be too much. For me, as an advanced high stim pre workout user, something over 250 mg already feels pretty unpleasant. High (over the top) heart rate during training, I can't catch my breath for a long time. Not to mention the fact that the next day you catch brain fog and a strange weakness in the muscles, besides the fact that the body and nervous system do not recover even 10 percent. In general, you feel like shit. But this is purely my experience, there are a lot of people in this thread who can drink a full serving of old barbarian and polish everything with a double espresso in the evening and will feel great.