I remember some similar threads before, so you may find some info if you look long enough. Rolling Changa / enhanced leaf joints can be a good way to introduce yourself to spice without it being overwhelming, but I think you'll soon see it's kinda pointless and a waste of your material. I certainly wouldn't want to be taking a walk around with it - it doesn't lend itself to that type of experience IMO.
I have rolled a few changa joints though - dosage / ratios etc is down to you. I would suggest you put 2 full doses (say, 80-100mg spice) throughout your joint. The amount of mixer you have is personal preference. You might consider using a good rolling tobacco (if you don't mind smoking it) as a good medium to keep it smouldering and for the fuller flavour. Changa blends taste OK, but are nowhere near as nice as weed or tobacco IMO.
I remember reading of 1 memebr who would load a full dose into an area of a joint he could smoke in 3 or 4 pulls. He was able to get a near breakthrough dose with this method, but it will be very inefficient. You also have a situation where you may become incapable while still having a lit joint in your hand - not very safe.
Try a couple of changa joints if you feel the need to, but you aren't going to get anywhere near a full experience with this method. Good luck.
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