One source suggests that a good starting dosage for San Pedro is about 1 pound (about 450gm ), or about 45 gm dry. They also stated that a larger dosage would be much more desirable after mescaline content has been established.Many people are disappointed with their first excursion into the Cactus wonder world because of taking an initially sub-standard dose. It has been calculated that if a person takes a ineffective dose, the next dosage can be increased by a factor of 7 without pushing the range of toxicity. That is, if your first batch ingested was 20 grams and you felt no effect, you should be safely able to try 140 grams next time without ill effect. My personal opinion is that this is a bit on the excessive side. Better to play it safe and work your way up slowly. If you try to fly and fail, you will probably want to give it another shot. However if you take an excessive amount and have a bad trip, it may scare you off of hallucinogens for life. Think about it before you decide how much to try.Often times determining the approximate dosage of a section is rather difficult, especially if you don't have a set of scales. To help you figure out how much weight you have for a given size section, here are some figures.1.5 - 2.0 inch diameter section = 1.0 ounces per inch of length2.0 - 2.5 inch diameter section = 1.5 ounces per inch of length.2.5 - 3.0 inch diameter section = 2.0 ounces per inch of length3.0 - 3.5 inch diameter section = 2.5 ounces per inch of length3.5 - 4.0 inch diameter section = 3.0 ounces per inch of length4.0 - 4.5 inch diameter section = 3.5 ounces per inch of length
You can find live ones in the garden section of Home Depot and Lowes.
From my fellow psychonauts, they commonly use 8-12". Most of these cactii have a pretty low alkaloid content, about 0.08-0.5% by dry weight, but the bulk of the alkaloids are mescaline. There are a number of ways on line to isolate the good stuff out. Mescaline isn't the most potent of actives you will run into and when you consider you need 8-12 peyote buttons for a dose, you are looking at 120-180 mg--roughly 12" of most Echinopsis species. Plants grown in full sun with a long history of scarce water and slow growth tend to have the most alkaloid content. Simple water extracts will often make you feel pretty bad at first and even relatively purified mescaline has a tendency to make one feel sort of ill at first, but the experience after that is almost universally benign, way less intense than other common psychedelics like LSD. Colorful visuals and sound distortions are common and visuals are often startling. Mescalito can be a powerful teacher, especially if you are in a stress free and safe environment and your mood is open minded and calm. There are lots of good trip reports on Erowid and they seem pretty accurate, IMHO.