No, they definitely act. This misconception persisted for a very long time and there was no technique to demonstrate the same. But new researches show that dilutions definitely act. For example:

1. When rats are drugged with the substance Arsenic, they excrete the same in the urine to a certain EXTENT. When these rats are given potentised Arsenic the rate of excretion increases considerably; and higher the potency, the faster is the elimination.
2. Another experiment showed that when homeopathic Belladona potentised) was given to GUINEA pigs, it produced contractions in the ileum (part of intestine); and higher the potency STRONGER was the contraction.
3. Though this is yet a hypothesis, it seems that beyond Avogadro's number, the molecules in solutions appear to develop a 'stamp' or 'image' of the original substance, which does not GET wiped off even in extremely diluted preparations.
4. As the proof of pudding is in eating. Proof of effectiveness of homeopathic MEDICINE is in results. Once you see good results you are convinced about its efficacy.

No, they definitely act. This misconception persisted for a very long time and there was no technique to demonstrate the same. But new researches show that dilutions definitely act. For example: