Yes there are a few factors that you could associate with 'healthy' or 'least unsafe', and they are hard to compare - apples and pears:
- The therapeutic index was mentioned
- Side-effects and toxicity were also mentioned: some benzo's come with additional toxic properties other benzo's may not have.
- Selectivity: if you take something like pyrazolam for anxiety, it's possibly one of the best ways to target it since you can avoid both the direct side-effects like sedation as well as the inverse when you withdraw from the drug. So if you 'must' take a benzo it is best that it does as little as possible while meeting the requirements for being effective for your needs. I really hate psychiatric medications that are like carpet bombing when you only need a sniper. Also you probably want the least affinity for the gamma2 GABA subtype since that is associated with physical dependency. You also want benzo's that don't act (much or at all) on IIRC alpha5 since that mostly fucks with your cognition / memory. (That may be answer to question in the OP but unfortunately I can find no information about different benzo affinities for alpha5, or alpha3 and 5 together - which would be the measure for association with effects on cognition etc). This could be mentioned under the previous bullet: side-effects since I don't think your cognition or memory being fucked with is EVER desirable unless you abuse benzo's to forget shit.
You can't very well suggest benzo's that properly follow the above criteria without stating what you need the benzo for.
For anxiety pyrazolam seems great because it is so selective for that (but it is not a prescription drug), for sleep arguably the Z-drugs are better because they are selective (however they may also be slightly carcinogenic although not so seriously that a significant number of subjects get that - everyone would be outraged and e.g. the FDA would shut it down - same goes for those nitrobenzodiazepines: the harmful effect may be there but I can't imagine the odds of getting cancer from it to be but slim.
Also pretty much all the hypnotic benzo's also have high potential for physical dependency having both high alpha1 AND gamma2 affinity.
Like Z-drugs such as zolpidem/ambien, benzos are not meant to be taken long-term anyway and if you do that regardless, minor carcinogenicity will probably one of the least of your worries to be honest.
For anti-convulsant effect I think I would say diazepam since it has high alpha3 (anticonvulsives) affinity without having the bad high gamma2 (physical dependency) affinity like many of the others that have high alpha3 affinity, for muscle relaxation nitrazepam is very effective (most of all I tried) despite being a nitrobenzodiazepine. I'd say it's sort of selective for that.
Memantine? Intersting handle, OP.
Benzodiazepines are remarkably healthy, really. In an acute setting, not combined with other substances (especiallys CNS depressants) you really can't go wrong. The lethal dose is going to be exponentially higher than what would be required for sedation/anxiolysis or whatever it is you're desiring.
The dangers of illicit or otherwise unsupervised use of Benzodiazepines come in a few different forms. Now, the anti-inhibitory nature of this class can cause you to do stupid, dangerous shit that you otherwise would not do, like driving a car, or punching a mounted-police officer's horse during a 4th of July parade. Also, when combining Benzo's with the aforementioned CNS depressants, like Alcohol or Opioids, your chances for an overdose increase significantly, as do your chances for dangerous inhibition.
In a chronic setting, dependence becomes dangerous when your supply runs out. "Cold-Turkey" withdrawal is acutely harmful to the brain and body, not to mention the fact that it's an extremely unpleasant process.
In short, if you're abusing Benzodiazepines chronically, you are asking for a lot of unnecessary trouble and hardship. The withdrawal syndrome of both Benzodiazepines and Alcohol is more traumatic than that of say, Opioids, with a lot less of the initial pleasure. If you're just dabbling occasionally, you should be fine, just don't go combining them with other drugs and make sure to avoid taking them everyday. The safety profile is pretty similar from Benzo to Benzo, the one factor that makes one more likely to be dangerous is the onset/duration of effect and to a lesser extent, the half-life. So, a short acting Benzodiazepine like say, Triazolam (Halcion) or Alprazolam (Xanax) is more likely to make you act a fool or OD, given the fast, hard punch they deliver.
I don't know which are the safest but I can certainly will tell you which ones are the worst (IMO & IME) in terms of cognition and long term organ damage.
The absolute worst especially for cognitive function & for long term organ damage:
1. Lorazepam (with small to medium tolerance, any dose above 2mg+ will provide extreme amnesia). I've tried more benzos than I care to admit and I've never encountered another benzo that produces this much amnesia at a medicinal dose.
r!