The addiction syndrome is quite similar across different addictive drug types, reflecting a shared pathway of pathological changes within motivational circuits that increasingly prioritize drug acquisition and use. This neurobiology, and drug addiction symptomatology, overlaps considerably with behavioral addictions (e.g., gambling disorder). However, addiction is distinct from symptoms and mechanisms underpinning intoxication and withdrawal, which are diverse and unique to each drug class. The intoxication phase is followed by some degree of withdrawal, manifesting clinically as opposite to intoxication, reflecting a homeostatic response to it. Withdrawal has a quality, duration, and dangerousness that depends on the individual, the drug type, and drug use history. Heavy/chronic patterns of use in addiction can produce longer, more severe withdrawal phases, but addiction and withdrawal can exist separately. How a drug acts upon different receptors and other downstream brain systems (pharmacodynamics) impacts the strength of its psychoactive (intoxicating) and motivational (addictive effects). Meanwhile, the route and rate of drug intake and its breakdown and elimination (pharmacokinetics) can also impact intoxication, withdrawal, and addiction risk. With addiction, the patient becomes tolerant (insensitive) to the intoxicating profiles of drugs they like, whereas their motivation, craving, and wanting to use the drug sensitizes (grows pathologically).