There is a large gap between players' role play interest in drugs (which this census marks to be "high") and their actual end-user consumption in the script (low). Bluntly put, many people likely would rather portray the drug dealer who wins instead of the drug addict who doesn't. Addiction is also a difficult thing to portray properly. These are both things that will probably always come through in drug RP and elongate the duration of the supply chain,
That said, I believe if the gameplay applications of drugs were different by script, they would find wider use. They currently serve, as a whole category, two active purposes and provide one detriment.
Active Description: They create descriptive lines to be read on /examine, saving the player the trouble of continually updating a set of symptoms.
Active: They buff your health.
Passive Detriment: Addiction makes you lose HP.
Health buffs are useful in combat, that's about it. This leads to a specific type of demand that encourages end-of-chain buyers to stockpile, specifically ones engaged in violent crime. Drugs are something they want to have for themselves and their people when needed (like when you're about to engage in a conflict), and don't want to a. forego at an IC loss to themselves (selling for less than they bought the items) or b. abuse ICly to the point where it becomes a detriment to their character and/or ability to operate in combat. At the end of the chain, just because of how drugs are designed and tend to find their application in the server among most chains, there is a disincentive either to sell them or personally abuse them.
There is also little variety between drugs. They primarily serve the same functions, with tweaks on the extent to which they buff a player and consequently debuff them. This leads to a hierarchy of drugs which somewhat accurately mirrors real demand: "soft drugs" that don't leave damaging impact relative to their buff tend to be the ones in high demand and circulation.
I think an easy fix would be to acknowledge the purpose that most drugs currently serve on GTAW is for combat, but that all drugs don't need to do that. And to that point, if crack cocaine suddenly offered a nutty temporary buff, were reasonably priced at the distributor level, and found high quantity of distribution, the shit would be all over Davis RP.
I think a holistic drug system could look more like this. I'm not sure how feasible these tweaks are, but I trust our developers! I believe the potential of passive effects has been massively underexplored.
Active Description: This is good as it is. If anything, I'd encourage fleshing out each level of addiction by substance with more unique descriptors.
Active: Some continue to increase total HP. Some increase the movement speed of your character (+/ 5%, a small change). Some temporarily increase your melee damage (maybe PCP). Active animations/intrusive screen effects should return for psychoactive drugs like psilocybin or LSD. That's just part of the subjective experience.
Active Detriment: Some drugs reduce movement speed. Some drugs reduce melee damage (fragility, physical fatigue). Some drugs force the player into particular walkstyle animations for the duration of effects. Personally, I'd consider that a benefit for an RPer, but the combat-focused would look upon a PCP-frantic animation as a detriment. It's still faithful to the drug experience and loss of control.
Passive: Some drugs increase total possible HP for the duration of addiction. Some drugs increase melee damage for the duration of addiction (small % buffs possibly in a tiered fashion, think steroids, progressing in physical strength).
Passive Detriment: Some drugs decrease total possible HP for the duration of addiction. Likewise, some drugs decrease melee damage for the duration of addiction, which I believe would be a realistic passive detriment for many drugs. Some drugs decrease movement speed passively through addiction. Some drugs should leave character descriptions beyond their active effect. A heroin addict is still distinctive even when they are not high.
If there is going to be demand for each unique drug on the market, they should provide objective and subjective effects in novel, unique combinations. Otherwise, they will continue to be relegated in an objective hierarchy based on their end-user pros versus cons, all based around combat. Drugs that are already scarcely circulated will continue to be stockpiled and sought in lesser quantities if they remain objectively inferior to other drugs in a system that revolves around a very small table of benefits and detriments.