Endorphins are ENDOgenous mORPHINes i.e. endogenously produced morphines. These chemicals (also called neurotransmitter) are produced in our brain and suppress the pain, provide a sense of calm and comfort, etc.
No medicine is known to release endorphins (although some like endorphinate may contain receptor switchers to enhance the production of endorphins). These neurotransmitters are endogenously produced during times of stress, after exercise, etc. They are also released when the right locations in the brain are stimulated by electrical (including binaural sounds) or chemical means. Consumption of alcohol, certain steroids, heroin and other opiates are known to alter the endorphin release in our body.
Since, other conditions such as physical exercise, depression and anxiety can cause release of endorphins; any experimentation involving drug-induced endorphin release will need to control these conditions. In other words, the subjects need to relaxed, should not have depression and should not have exercised prior to experimentation. In other words, any other condition or state that may cause endorphin release will have to be controlled in the experimentation.