Final answer:
The commonality among addictive substances such as alcohol, marijuana, and cigarettes is their effect on increasing dopamine activity in the brain's reward system, which can lead to substance use disorder.
Step-by-step explanation:
The common thread that ties addictive substances such as alcohol, marijuana, and cigarettes together at the level of brain function is their interaction with the brain's reward system, particularly affecting the neurotransmitter dopamine. Although these substances interact with different receptors—alcohol affects the NMDA and GABA-A receptors, marijuana affects the CB1 cannabinoid receptor, and cigarettes affect the nicotinic receptor—they all ultimately lead to increased dopamine action in the brain.
This increase in dopamine is a critical aspect of the brain's reward system, promoting feelings of pleasure and reinforcing behaviors, including the use of addictive substances, despite negative consequences. Psychoactive drugs like these may also lead to adaptations in neurotransmission over time, potentially leading to tolerance, dependence, and substance use disorder.