Its probably easiest for me to sort it in the different psychedelics as each have their own usage pattern and health benefits / disadvantages.
LSD: I've been doing LSD roughly once each month for the past four years, with the occasional exception of doing two trips in a month or even two in a week, usually those moments are rare and its really quite strictly once a month. I chose that a while back to prevent ány tolerance (I don't have any, my trips are just as intense as they always were) and to have each trip still feel special because there are so many sober days in between, this works really well for me. I have no flashbacks or HPPD or any negative effects whatsoever, and there are even some positive sides; like a positive afterglow that leaves me more motivataed for up to two weeks, and a lot of insight in my own person and conciousness which has helped me grow as a person, not to mention the great memories, inspiration etc. that I get from it.
Mushrooms: Haven't done them in years, but back then I used to trip on them every three months or so, if I'd do ány more I'd get actual HPPD that wouldn't go away for atleast six months, even with the well spaced trips I had nearly continous flashbacks for a few weeks after each trip, although mushrooms álso gave the biggest benefits; a phobia completely disappearing in 2006 and nót returning for example, and the most intense personal growth; I can't think of any substance I learned and gained more from then shrooms, but they also give me the most flashbacks / can too easily cause HPPD in me. I think this is all because I'm extrémely sensitive to psilocin, 1 gram of fresh mushrooms gives intense visual and psychological effects, higher doses can lead to egodeath lasting up to 10 hours. I have low body weight and get more visuals from ány substance then most people I know, but this is most extreme with mushrooms.
2c-b: Only tried recently but have done 4 times now, that typically also had a month in between, this combined with LSD makes for 1-2 trips a month as sometimes I'll just combine the LSD and 2c-b in one trip, which works well too. 2c-b has given me no negative side effects ever, not in the short or long term, and no HPPD or flashbacks either. It shares its afterglow with LSD but I find it the least 'deep'; its more euphoric fun with neon patterning static then a real trip, but I like the substance nonetheless, recreational value is also valuable to me.
Dissociatives: Not psychedelics, but can be seen as psychedelic. I get visuals from these and interesting changes in thoughtline and creative thoughts so they can be interpreted as psychedelic. I do two dissociatives; ketamine and nitrous, both with their own usage pattern. Ketamine is on average once a week but there are exceptions both ways, sometimes I leave 2-3 weeks in between while at other moments I do it 2-3 days in a row, average once a week though. Positive effects from this are a long afterglow, up to more then a week which is strong and which is, I assume, its antidepressant effect. No negative other then a slightly deminished skill to remember words for 1-3 days after a heavy binge, this always restores completely within one week and I blame metabolites still being in the blood. I'd rather keep usage down to twice a month but I'm too easily persuaded into doing some, even by myself. I wouldn't call it addicted, just véry very fond of the substance, but health seems to be absolutely normal if not better then ever recently so its not a problem.
Nitrous has a more random pattern, no health benefits or problems noted ever but I pay attention to my health and take enough vitamine b12 around nitrous binges, it ranges from once a month to three times a week depending on if I have any.
The only real 'permanent' negative health issue has to do with smoking hash; my lungs are a bít more sensitive to bronchitis-like coughs but if I sleep well and consume a lot of vitamin C I don't get it at all, its just that befóre smoking I never had bronchitis, after starting weed and hash I got it a few times a year and after starting with a daily 1 gram vitamine C intake, I haven't had it
Still, my lungs can't be too healthy; smoke is bad.
The classical psychedelics have had only positive effects and dissociatives a lót more positive then negative, and the only negative being relatively short term and very minor, so I'm pretty happy with my usage patterns and hope to keep them this way.
