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Bummer with the IBS, but Congratulations on transitioning off of the Xanax and opiates: your inner self has already begun to regrow itself, and will proceed naturally with time

Salvia is quite strange normally. I have found its experience to make sense only on rare occasions. It is similar to DMT in that it provides completely immersive transport to another realm (although: different realms, different feelings, different pretty much everything). That, and they both cause sigma-1 receptor activity at high enough doses

The Nexus has a great scientific community, researching publications or just finding cool info will definitely be welcome here

I would strongly encourage reading everything you can get your eyes on about these plants and chemicals 

before you even think about ingesting anything!

[I don't mean to be off-putting, just emphasizing words of caution to someone new to these things]

Curiosity and patience are very helpful in working with entheogens and psychedelics. Read all you can from this forum, check out erowid.org and lycaeum.org for other information (both quite useful sites). Your being a researcher will go wonderfully with the investigation of these things, many have found that absorbing all the information they possibly can about a molecule before going anywhere near it generally reduces the potential dangers and makes the experience more comfortable and rewarding.

That all being said, nothing will quite prepare you for DMT -  but it is also never a good idea to approach anything unprepared

An experienced trip sitter can be nice. It helps to have someone there to reassure you, especially if they know what you're going through. Otherwise, a really good friend can sit with you as long as both of you research what the common effects and duration are. I think there's guides for trip sitters out on the web, have your sitter-candidate read through what you can find as well as a few experience reports for the item in question.

Some people will recommend different avenues of initiation, but I think a nice and low dose of mescaline containing cactus is an excellent introduction (this is definitely just a personal opinion). It does last a long time (10-12 hours with a 1-2 day 'mental fogginess'), but the experience is generally inviting and controllable to a degree. Read the Cacti sub-forum here and check as many other sources as you can find.

Stop by the chat room after you've read up a bunch, there will probably be a few knowledgeable people in there who'll be happy to share

Welcome, Good Luck and Happy Trails 8)