It's not as simple as to which one specifically. Many neurotransmitters can cause euphoria, and or cause the release via modulatory action. However, dopamine is one of the most connected to euphoria. There are also Endocannabinoids, Gaba, Acetylcholine, Dopamine, Endorphins, Anandamide, and peptides.
acetycholine
Excitatory neurotransmitter
Salvia
Abuse of substances such as cocaine, amphetamines, and heroin have been linked to the neurotransmitter dopamine. These substances can increase dopamine levels in the brain, leading to feelings of euphoria and reinforcing the cycle of abuse.
The neurotransmitter epinephrine can cause the blood pressure to become low. This neurotransmitter also regulated the heart rate. It is often controlled by stress.
inhibitory transmitters
Beta 1 receptors
Morphine causes a reaction to receptors in the brain causing you to feel dizzy, sleepy and even euphoric.
What causes one to overamp when using meth amphetamine is usually the need to get in the euphoria fast
Acetylcholine is the primary neurotransmitter responsible for muscle movement. It is released from motor neurons at the neuromuscular junction to stimulate muscle contraction.
True. Cocaine causes the sudden release in the brain of a neurotransmitter called dopamine. Source. Prentice Hall
The neurotransmitter that causes an individual to feel more alert is norepinephrine. It plays a key role in the body's fight-or-flight response, increasing heart rate, blood flow to muscles, and overall alertness.