Final answer:
Tolerance and withdrawal to psychoactive drugs occur as the body's attempt to maintain homeostasis, with tolerance requiring more of the drug to achieve the same effect and withdrawal involving negative symptoms upon cessation.
Step-by-step explanation:
Tolerance and withdrawal to psychoactive drugs are best understood as the body's attempt to maintain homeostasis. Tolerance occurs when a drug user requires increasing amounts of a drug to experience the effects previously obtained at lower doses. This physiological adaptation can lead to the user consuming dangerous levels, increasing the risk of overdose and death. Withdrawal, on the other hand, involves a range of negative symptoms experienced when drug use is discontinued, with symptoms often being opposite to the effects of the drug.
Physical dependence involves bodily functions changing to adapt to the drug, while psychological dependence includes an emotional need for the drug, often to relieve psychological distress. Both aspects can contribute to addiction and the compulsive use of a drug despite its negative consequences. Rehabilitation often includes psychotherapy and sometimes the use of other psychoactive drugs to counteract dependence.