For me, I'd have to say methamphetamine. One night of sort of heavy use but not something other Bluelighters seemed to regard as uncommon (and I mentioned my lack of tolerance) for an evening and night smoking meth left me feeling far more depressed for at least 2 or 3 weeks and it was maybe a little longer before I felt sure I suffered no noticeable brain damage.
That was one night. Another time before this was not as bad but still not good at all.
I smoked meth with my brother earlier. It hasn't worn off, my dose was lower, and I am getting the feeling it is doing the same bad thing as last time. Still feels good, but I can tell by the way it is changing, at least I think.
^rollinlikeroyce
I wouldn't be sure MDMA could not be as bad if used too much. It only had positive after effects for me but I did not use it much and would just take a small or no redose each time. I have heard of people being profoundly depressed for a long time to possibly never return to normal after severe long-term abuse. People rarely use those with the frequency of meth, crack, or heroin. If they did, I think it would be every bit as damaging. Heroin may be the least bad as far as permanent damage if you practice safe techniques. Meth is neurotoxic. Crack may be, though I have heard on Bluelight from many that cocaine isn't neurotoxic. It is cardiotoxic and the repeated, significant, rapid elevations in blood pressure from smoking crack would probably leave one prone to strokes and heart attacks long after the person is clean.
It may be that much of the neurotoxicity (at least measured by serotonin activity) associated with MDMA use could mostly be avoided by taking high doses of antioxidants at the right times in the experience but that was I think in rat brains.
You should probably avoid meth, cocaine, and heroin completely. These types of drugs are not that much fun. Tripping is fun. Drugs that make you laugh and smile and feel really happy and in love with the universe are fun. Drugs that make you feel comfortable or pleasant but offer no excitement and do not actually make you happy in a positive, emotionally uplifting way that won't leave you feeling emptier or deader inside the following day than the day before are at most good for rare times when you might not make it any other way - they won't help you forever.
Drugs that are enjoyable or personally enlightening and leave you feeling better or at least not worse once it is over should be considered a positive thing in one's life so long as you know as much as possible about what you are doing. If it feels good and then you suffer for it the next day(s), it wasn't worth it, more pain than benefit. You sure don't want to get addicted - much of the time you'll probably be using to keep from getting sick (I do that when I am low enough on opiates or benzos) and it stops being fun. I don't enjoy hydrocodone much until I get to at least 90mg and to get quite nice effects I'd need closer to 150mg. 60mg morphine by IM injection is better than the hydro. I know heroin is stronger, but I am sure it stops being fun too and I'll bet harder to withdraw from than poppies or hydrocodone (experienced those two).
I hope opiate use is making my depression worse (though I was depressed as a kid, long before drugs with little break in it) because then quitting could make it better. Intend to try ibogaine before long as I am so depressed I can't tolerate reducing my dose but ibogaine may help some of that/prevent any major withdrawal symptoms.