For an efficient gas exchange, the respiratory membrane must be 0,5 to 1 micrometer thick. That way gases are able to penetrate the membrane and get to the blood capilar as fast as possible. If the respiratory membrane was thicker, gases do not penetrate and go through the membrane as fast and efficient as in the previous case.
I believe it's amphetamines. They release chemicals called catecholamines, particularly dopamine. Tolerance to these build very fast making them highly addictive.
