This is also a good idea why it is prudent to stick to proven ayurvedic and TCM recipes that have been used and are known to be synergistic and low toxicity.
If you know any kind of pharmacology and botany, you will begin to understand how 1+1+1 can = 10 and get you in a whole lot of trouble. I know some forums where people use and create recreational herbal formulas ( in other words hallucinogens). Suffice to say they take things that are normally considered deadly, but they do so in a manner that is below the toxicity threshold. They KNOW their Science and dosing, and they understand the Science behind the herbology.
When you start mixing herbs that are not known to be mixed, you are messing around with something that is going to be very unpredictable.