The drugs posing the most immediate risk of
Organic brain damage are

I'm not sure exactly what your question is here because your title doesn't match what you have written in your post.

Much less

What class is this question from?

All effects drugs, alcohol even tobacco causes damage to your body and brain, if your speaking of specifics, like -LSD, this leads to impaired learning and memory abilities, -Meth, activates certain systems in the brain is very addictive, -inhalants, fatty tissue protection in nerve cells are destroyed this stops or slows down neural transmissions. - Estasy, destoys certain brain cells, the cells that are damaged can't reconnect normally, -Heroin, brain cells become dependent on this drug and the user needs it in order to function. Marijuana, the part of the brain that controls emotions, memory and judgement are affected, weaking short tem memory and can block information making it into long term memory. And the last one I can think of is Alcohol, very addictive, loss of interest in just about everything, eventually, effects receptors in the brain to reduce ability to feel pleasure. Just a few...

The theory that ecstasy destroys brain cells has been debunked by scientists. Click here for the source (http://www.bmj.com/cgi/content/full/313/7054/423/a).

Heroin/Morphine and other opiates in pure form have very little or even no long term damage to the brain or the body. Addiction is the biggest issue with this group of drugs.

Cocaine, though a powerfully reinforcing drug, is not believed to cause brain damage. However this is disputed. Cocaine is the worlds most psychologically addictive substance, according to studies.

Here is a scientific study on cocaine's addiction ability:


It has been shown in studies that rhesus monkeys, provided with a mechanism of cocaine self-administration, prefer the drug over food that is in the cage. This happens even when the monkeys are starving. Female monkeys with offspring abandoned their young upon being introduced to cocaine, and in a few cases, mothers killed their offspring. In all cases, a monkey aggressively protected the apparatus which delivered the cocaine, and in most cases, fights to the death between monkeys occurred to secure access to cocaine. The monkeys who self-administered cocaine, did virtually nothing else. Complete disregard for food, sex, sleep, water, hygiene, offspring, and life in general was always the case for those monkeys addicted to cocaine. Marked behavioral toxicity was also apparent in all monkeys addicted to cocaine. Monkeys that were provided with a mechanism of heroin self-administration also self-administered it indefinitely, but when starved, the monkeys on heroin chose food and water over heroin without hesitation, unlike those monkeys on cocaine who consistently chose the cocaine over food, despite the fact that some were near death by starvation. Some monkeys which were deprived of water and then given the choice of cocaine or water, chose cocaine without hesitation. Those on heroin also continued to care for, and be protective of their offspring, they slept, and showed that they cared about their hygiene by grooming themselves continuously. Protective or aggressive and/or violent behavior over the removal of the apparatus which provided the heroin was not observed, as was seen with cocaine. Unlike the monkeys put on cocaine, the monkeys that were put on heroin were easier to manage and deal with. Only a very small number of monkeys became irritable and aggressive upon removing the apparatus which delivered the heroin. Within the cocaine group, all monkeys became enraged and violent upon the removal of the apparatus which provided them with the cocaine. Several monkeys tried to break free of their cages, others became psychotic, bouncing around in their cages, shrieking loudly, and some even began to bite pieces of their arms and legs. One monkey cried for several hours, while at the same time mutilating his arms. No other major drug of abuse has shown a capacity to produce an addiction as extreme as has cocaine.

Cocaine addiction continues to be the most difficult to manage, and according to some scientists, addiction to cocaine may be almost impossible to stop. Relapse rates among cocaine users is in the range of 94-99%, by far the highest among all common drugs of abuse.


[SOURCES]

Yuferov V, Butelman ER, Kreek MJ (2005). "Biological clock: biological clocks may modulate drug addiction". Eur. J. Hum. Genet. 13 (10): 1101–3.

Science, Vol 201, Issue 4355, 534-535

Aigner TG, Balster RL. “Choice behavior in rhesus monkeys: cocaine versus life” Science 201: 534-535.


Methamphetamine and dextroamphetamine do cause brain damage. Meth gets all the publicity, but most people don't realize that studies have actually shown dextroamphetamine to be more reinforcing then methamphetamine in studies done on monkeys. Regardless, these drugs are pure evil. Brain damage should be least of an addicts worries, because the very soul of the addict is taken away by meth or dex. They don't eat, which turns them into walking zombies (literally), they don't sleep (which makes them go insane), and they become angry, violent and even homicidal and suicidal. These are the worst drugs on earth, even if they are less addictive than cocaine is (well according to the studies, at least).

But I am going to make another post about commonly prescribed drugs that will cause brain damage and other serious effects...

Now, you would all be surprised, but certain benzodiazepines have been documented causing organic brain damage, speech disorders such as stuttering and cluttering, aphasia, dysnomia, delusional disorders, severe memory problems, motor coordination damage, and neurological problems. Along with those, cognition problems and balance disorders are common.

But now, don't worry. The common benzos most people get don't cause any of this.

The ones that do however, are the ones that hypnotics (not all benzo hypnotics though, just a few evil ones) which are highly abused, are ultra-powerful benzos, and they are:

Temazepam (Restoril) (http://en.wikipedia.org/wiki/Temazepam)
Nimetazepam (Ermin) (http://en.wikipedia.org/wiki/Nimetazepam)
Nitrazepam (Mogadon) (http://en.wikipedia.org/wiki/Nitrazepam)
Flutoprazepam (Restas) (http://en.wikipedia.org/wiki/Flutoprazepam)
Triazolam (Halcion) (http://en.wikipedia.org/wiki/Triazolam)
Flunitrazepam (Rohypnol) (http://en.wikipedia.org/wiki/Flunitrazepam)
Flurazepam (Dalmane) (http://en.wikipedia.org/wiki/Flurazepam)

The above are the most powerful benzos, though the ones listed below are also among the strongest of benzos, they aren't listed among the others up there because they do not cause the brain damage or other disorders these particular benzos cause. Well, at least it is nothing in medical literature has suggested that they are toxic.

Lormetazepam (Loramet) (http://en.wikipedia.org/wiki/Lormetazepam)
Loprazolam (Dormonoct) (http://en.wikipedia.org/wiki/Loprazolam)
Brotizolam (Lendormin) (http://en.wikipedia.org/wiki/Brotizolam)
Midazolam (Versed) (http://en.wikipedia.org/wiki/Midazolam)
Estazolam (ProSom) (http://en.wikipedia.org/wiki/Estazolam)


Alprazolam (Xanax), Clonazepam (Klonopin), Diazepam (Valium), Lorazepam (Ativan), and other common benzos are like M&M's compared to the ones above.

From my literally brain dead friends and neighbors that do drugs I truly believe it is mainly the combination of drugs and alcohol they do. Many do their drug of choice, drink, smoke weed and do pills. Mixing uppers with downers and alcohol and all the other drugs has to have some adverse effect on your brains chemicals.