Amphetamine like adderall,vyvanse are weaker because they do not have a methyl group. adding a methyl group to amphetamine makes N-Methylamphetamine. a Methyl group makes it much more potent therefore you need less to get high and it is much more powerful.
for more info go to
https://psychonautwiki.org/wiki/Adderall
https://psychonautwiki.org/wiki/Meth
Answer: Endorphins
Explanation: Endorphins are chemicals secreted by the brain also known as neurotransmitters that send electrical signals inside the nervous systems.
The factors that initiate the secretion of endorphins are stress and pain.
When endorphins are secreted they reduce feelings of pains, and in runners that cause a phenomenon called " Runners high" which allows runners to keep running without feeling pain or stress.
Depends on genetics, past attempts, there’s not a straight precent there’s a lot of factors.
First is the brain, spinal cord, and heart begin to develop. Then A blood vessel forms which will later develop into the heart and circulatory system.