Is D.A.P. A Drug?

DAP (Dog Appeasing Pheromone) is a manufactured substance that replicates  a naturally occuring phenomenon. All lactating females release substances called "appeasing" pheromones, the function of which is to reassure their offspring. As the young animal faces all the terrors of its new world, the pheromone manufactured by its Mum brings it a degree of calm and serenity.

Here's a technical explanation taken from the website of CEVA, the manufacturers of D.A.P., but don't ask me to translate it into understandable language

"Dogs perceive pheromones with their vomero-nasal organ (VNO). This paired organ, situated above the hard palate, opens into the incisive canal, which connects the mouth cavity with the nasal fossae. Stimulation of the specific receptors leads to depolarisation of the vomero-nasal nerve which connects the VNO with the accessory olfactory bulb. Subsequently, different connections stimulate different structures within the limbic system, thus altering the emotional state of the dog."