Is it harmful to mix certain herbs, like horse chestnut, butchers broom, and bilberry?
This is "Your Herbalist"....
Hey, mixing herbs is an art and science and... certainly I would not recommend it as favorite pastime for a lay person.
Not because the herbs you're blending will harm you (although that too). The reason is two fold:
the purpose behind mixing herbs is either:
a) to amplify their desired, select medicinal action
b)to cancel out/counterbalance any unwanted medicinal action
You can learn how to properly mix herbs in a Herbal College, or...
...and this is much easier...
you can rely on a reputable herbal company, who employs on-board scientific team of pharmacognosists.
Pharmacognosy is like pharmacology, but involves botanical materials: healing plants. Those guys are very highly trained specialists, they also do know about blending various herbs.
Now, you're specifically asking about horse chestnut, butchers broom and bilberry.
Yes, in fact these herbs cam mixed or taken together (if that's what you mean).
Here's an example of just that: horse chestnut blended with butcher's broom and couple of other ingredients: fenugreek, rutin, hesperidin.
The idea was to create a powerful herbal combination to combat varicose veins and hemorrhoids, to name but few.
These herbs strengthen and nourish veins, minimize the appearance of varicose and spider veins, relieve painful leg conditions; provides anti-inflammatory and astringent benefits.
(click on the link below).
In math 2+2 = 4 (always), in herbology however
2+2 = 5 or 7 or just 3, depending on what's desired. And this is the beauty of it.
By the way, it would appear from your message that you're could be fighting one of the above conditions...
IF SO... please check this link. That's better than doing things yourself, unless you do have an experience.
All the best