Horny goat weed is called that due to the effect it has on hormones, especially testosterone. Men sometimes need a little help in that department, so they try herbs.
The problem is, this herb is a yang tonic in Chinese medicine. Yang tonics will strengthen your kidney energy and improve hormone production. Horny goat weed is NEVER used alone! This herb should be combined with other herbs that energetically balance it out.
If you take this herb too long, usually over 3 weeks, you can have too much yang and not enough yin. Yang is the hot and yin is the cool. If you take yang tonics too long, you can get insomnia, irritability, hot flashes and many other symptoms.
No reputable herbalist would sell Horny goat weed to people to take as a single herb. This herb should not be used outside of the care of an experienced herbalist.
If you are having problems with libido, there are other herbs you can take for that. Cordyceps is an example. Cordyceps is a kidney tonic that is both yin and yang. It can be taken long term and will increase your energy levels and libido with no side effects.
If you have already taken too much horny goat weed, you will need to see an acupuncturist for the fastest solution. If this is not possible for you, you could take American ginseng extract for about 3-6 months to nourish your yin and re-balance your body. You should take at least 2 pills 3 times per day.
In my opinion, horny goat weed should not be sold as a single herb. Herbs such as Ginseng are sometimes used to improve vitality and virility.