Herbal supplements are not regulated as food and drugs by the FDA, meaning people can sell them without any safety testing. As a result, many herbal products don't undergo clinical trials to determine their effectiveness in treating specific conditions.
Herbal supplement sales increased by 7.7% between 2016 and 2017 (from $6 billion annually). However, this number may be inaccurate because it doesn't include all types of herbs sold under these names. For example, some people use "herbs" as an umbrella term that includes everything from rosemary tea bags. These contain only trace amounts of actual rosemary all the way up through yarrow flowers.