Pentazocine, sold under the brand name Talwin among others, is a painkiller used to treat moderate to severe pain. It is believed to work by activating (agonizing) κ-opioid receptors (KOR) and μ-opioid receptors (MOR). As such it is called an opioid as it delivers its effects on pain by interacting with the opioid receptors. It shares many of the side effects of other opioids like constipation, nausea, itching, drowsiness and respiratory depression, but unlike most other opioids it fairly frequently causes hallucinations, nightmares and delusions. It is also, unlike most other opioids, subject to a ceiling effect, which is when at a certain dose (which differs from person-to-person) no more pain relief, or side effects, is obtained by increasing the dose any further.Chemically it is classed as a benzomorphan and it comes in two enantiomers, which are molecules that are exact (non-superimposable) mirror images of one another. It was patented in 1960 and approved for medical use in 1964. Usually, in its oral formulations, it is combined with naloxone so as to prevent people from crushing the tablets, dissolving them in a solvent (like water) and injecting them for a high (as orally administered naloxone produces no opioid-negating effects, whereas intravenous or intramuscular administration does). Use
Medical
Pentazocine is used primarily to treat pain, although its analgesic effects are subject to a ceiling effect. It has been discontinued by its corporate sponsor in Australia, although it may be available through the special access scheme.
Systematic desensitization can be done in vivo (with live spiders) or by getting the individual to imagine situations involving spiders, then modelling interaction with spiders for the person affected and eventually interacting with real spiders. This technique can be effective in just one session, although it generally takes more time.Recent advances in technology have enabled the use of virtual or augmented reality spiders for use in therapy. These techniques have proven to be effective. It has been suggested that exposure to short clips from the Spider-Man movies may help to reduce an individuals arachnophobia. Epidemiology
Arachnophobia affects 3.5 to 6.1 percent of the global population. See also
Apiphobia, fear of bees
Entomophobia, fear of insects
Myrmecophobia, fear of ants

References
External links
Stiemerling, D. (1973). "Analysis of a spider and monster phobia". Z Psychosom Med Psychoanal (in German). 19 (4): 327–45. PMID 4129447. National Geographic: "Fear of Snakes, Spiders Rooted in Evolution, Study Finds"