Final answer:
The risk of developing tolerance and physical addiction to hallucinogens is rare, especially when compared to other substances like central nervous system depressants or stimulants, which carry a much higher risk of both physical and psychological dependence.
Step-by-step explanation:
The risk of tolerance and physical addiction to hallucinogens is considered rare compared to other addictive drugs such as central nervous system depressants or stimulants.
Hallucinogens, such as LSD and mescaline, typically alter sensory and perceptual experiences and do not generally lead to physical dependency. However, they can still produce psychological dependence. They act on various neurotransmitter systems in the brain, with some like LSD acting as serotonin agonists, and others like PCP acting as NMDA receptor antagonists. Unlike substances with high abuse potential such as alcohol, opiates, or stimulants, hallucinogens generally do not cause the user to experience withdrawal symptoms, which are indicative of physical dependence. Instead, with hallucinogens, there is a greater potential for developing tolerance, where more of the drug is required over time to achieve the same hallucinogenic effect.
That said, the use of hallucinogens is not without risks, including the potential for dangerous behavior during altered states of consciousness or the occurrence of distressing psychological effects such as paranoia or hallucinogen persisting perception disorder (HPPD).