Random - the OP says she has 30c arnica pills. That means the original arnica tincture has been diluted by putting one drop in 100 drops of water, 30 times, and the resulting solution has been dripped onto sugar & lactose pills. There might be one atom of arnica left in the whole bottle, if you are lucky.
As Ben Goldacre explains: "Many people confuse homeopathy with herbalism and do not realise just how far homeopathic remedies are diluted. The typical dilution is called "30C": this means that the original substance has been diluted by 1 drop in 100, 30 times. On the Society of Homeopaths site, in their "What is homeopathy?" section, they say that "30C contains less than 1 part per million of the original substance."
This is an understatement: a 30C homeopathic preparation is a dilution of 1 in 10030, or rather 1 in 1060, which means a 1 followed by 60 zeroes, or - let's be absolutely clear - a dilution of 1 in 1,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000, 000,000,000,000,000.
To phrase that in the Society of Homeopaths' terms, we should say: "30C contains less than one part per million million million million million million million million million million of the original substance."