While any number of social, psychological, and economic factors contribute to methamphetamine (MA) addiction risk, numerous biological variables have also been identified.The broad goals of this dissertation are to explore the mechanistic correlates of selective breeding for MA intake. The intent of the first aim was to further characterize the receptor encoded by Taar1m1J. Previous work found that this receptor does not produce a cAMP response in the presence of agonist. I build on this by demonstrating the TAAR1 encoded by Taar1m1J binds ligand with drastically reduce affinity. Thus, responses to TAAR1 agonists, such as MA, in these mice are more likely due to impaired ligand binding. The second aim focused on the hypothermic effects of addictive drugs in the MADR lines.