Endorphins (endogenous morphine) which literally means "a morphine-like substance originating from within the body".
We are able to produce endogenous opioid neuropeptides, with help from our central nervous system and pituitary gland.
The principle function of endorphins is to inhibit the transmission of pain signals. They can also create a feeling of euphoria very similar to that produced by other opioids.
Stress, pain and prolonged exercise are some common factors leading to the release of endorphins. Endorphins have been suggested as modulators of the so-called "runner's high" that athletes achieve with prolonged exercise. That's why we can feel extremely invigorated and "buzzing" after an intense exercise session.
The answer is yes, we can naturally produce chemicals that can make us feel good and high, and this does not involve consuming an exogenous substance.
One way involves the release of our endogenous endorphins...
Studies of acupuncture and massage therapy have shown that both of these techniques can stimulate endorphin secretion. Sex is also a potent trigger for endorphin release, as well as some hardcore exercise as already described.
Interestingly, studies have also shown that the meditation can also increase the amount of endorphins released in our body.