I would only consider injecting a drug that was formulated to be administered in such a manner, I know that in one trial used an infusion of DMT that allowed the duration of the experience to be extended.
N,N-dimethyltryptamine (DMT) is distinct among classic serotonergic psychedelics because of its short-lasting effects when administered intravenously. Despite growing interest in the experimental and therapeutic use of intravenous DMT, data are lacking on its clinical pharmacology. We conducted...
www.nature.com
Interesting to note that acute tolerance is a major issue. You can keep increasing the plasma levels but the subjective effects didn't alter.
I've tried >99% pure DMT (stored under dry nitrogen) and I've tried 'Changa' and in my experience, either their wasn't enough DMT in the latter or whatever was added actually subtracted from the effects.
Given free access to DMT, I wouldn't bother with anything else. I bought some through a friend who worked at Kokopelli and his workmate leant over and noted 'Oh, hippy crack'. But 20+ years ago the mates-rates price was ƒ300/gram (£75/gram). But i knew who had produced it as well as where and how. No carcinogenic crud left in it. White needle-shaped crystals.
Anyone considering acquiring DMT needs to beware of people cutting it with 5MeO-DMT to increase profits.