I’m no psychiatrist, but you’re correct, prescribing of anxiolytics ( sedatives ) such as “ Valium “ is widespread ; dependence – physical and psychological, and tolerance do occur. This can lead to difficulty stopping the drug after taking it for more than a few weeks. Such drugs ( benzodiazepines ) have a known chemical effect on the brain. They are only indicated for short-term relief of severe anxiety with /without insomnia.
Hypnotics ( sleeping tablets ) likewise should not be prescribed indiscriminately.
Other drugs - such as antidepressants - acting on the nervous system commonly have side effects, some dangerous. The increasing number using them as “ recreational “ drugs probably have no idea - either of these effects, or exactly what they have purchased. They often mix them with alcohol, they’re intoxicated when they buy them, and once they’ve agreed a price, are unlikely to question the drug dealer about quality, at the time or later.
But this is off – topic in a thread about food making you happy!