Taking Horny Goat Weed in high doses or for a long period of time may cause side effects such as dizziness, dry mouth, vomiting, and nosebleeds, and it can interact negatively with some medications. It should not be taken by those with bleeding disorders, hormone-sensitive cancers, or low blood pressure. While Vitamin B6, also found in this supplement, is needed for metabolism and brain/nerve growth, there is no scientific evidence that it directly increases testosterone levels in humans.