This was statistically significant but the new drug doesn't appear to be a very good hypnotic. Some clinical trials compare single doses of drugs but this allows very limited conclusions to be drawn. It is preferable that several doses of a drug are evaluated so that dose-response curves can be plotted. Usually the logarithm of the dose is used so that the middle part of the curve becomes linear. What is much more important is selectivity i.e. the potency of the drug to evoke the desired response compared with its potency to elicit another response.
Clinical trials can assess the potency of a drug or compare two drugs.
Most of the information about selectivity comes from preclinical studies. The public is only slowly realising that there is some degree of risk attached to all therapies. In theory a drug would be targeted so well that it only had the desired effect even at very high doses. In practice no drug has absolute selectivity and, if the dose is high enough, additional effects will be produced. In addition, while a drug may be very selective e.g. atropine, an antagonist at muscarinic receptors for acetylcholine, the distribution of these receptors may result in a dry mouth and other unwanted effects when being used to paralyse accommodation in the eye.