kjb1891 said:
Problems getting dosage right? Are there any strong digestion problems? Longer come on compared to more purified forms?
You've pretty much covered the main drawbacks. Dose is probably the biggest problem - SWIM found his dried San Pedro powder gave a very nice mild-moderate trip at about 35-40 g in capsules. It took about 40 capsules - if you choose capsules, be sure to have something you like to chase them with! SWIM did not notice any nausea, but he drank a panax ginsing extract beforehand.
As for digestion problems, SWIM said the 35-40 g he took felt like a pound of lead moving through his digestive track. It never hurt though, just a little bothersome.
The come on time was very long. If I recall correctly, it took at least 2 hours. SWIM also says he didn't notice any effects until he ate a grapefruit (perhaps the acidity helped break down the cactus matter? Just speculating...). He knew it was working though when he started to see flashing lights in his peripheral vision, as though someone had put a fan in front of a light (similar to what happens with LSD, I believe).
One other drawback is that you can't purify out the non-
mescaline alkaloids, as well. If you have P. Torch this might not be such a problem. But particularly if you have San Pedro you may feel the effects of the other alkaloids.
Overall SWIM greatly enjoyed his cactus powder trip. If you have someone you can hang out with, have some good music to listen to, and can use it in a responsible manner in a safe environment you'll probably have a blast.
Addit: definately go with capsules. IIRC SWIM used size 00.