I discovered that the herb Ruta graveolens (herb of grace) significantly improved my overactive bladder symptoms (which is very similar to IC). In fact, even when I stopped taking Ruta graveolens, the big improvements that this herb made in my overactive bladder symptoms still remained for months, which I found interesting.
Ruta graveolens has both anti-microbial and anti-inflammatory properties, and either of these may be the reason why it worked for me. Leonardo da Vinci praised this herb, and said it enhanced his eyesight, and also his creative inner vision.
Note that Ruta graveolens should not be used during pregnancy due to the risk of miscarriage.