Final answer:
Dopamine receptor D4 promoter hypermethylation increases the susceptibility to drug addiction, particularly to cocaine and methamphetamine, which are linked to dopamine neurotransmission and have high abuse potential.
Step-by-step explanation:
Dopamine receptor D4 promoter hypermethylation has been recently studied to increase susceptibility to drug addiction to cocaine and methamphetamine. Studies have shown that stimulants like these increase levels of neural activity, particularly by acting as agonists of the dopamine neurotransmitter system. Dopamine activity is closely associated with reward and craving, making substances that influence dopamine neurotransmission, like cocaine and amphetamines, addictive. Methamphetamine use, in particular, has become widespread, with users seeking the euphoric high and intense pleasure it can provide. Prolonged use of these drugs leads to alterations in normal brain functioning, including the depletion of monoamine neurotransmitters and the reduction of dopamine receptor availability, as evidenced by PET scans of addicted individuals showing less dopamine receptor binding.