I don't know if there is anyway for it to be "instant" considering that it has to be metabolized and enter the blood stream, which invariably takes time. You may be able to increase the harmala dose in order to get quicker onset. I don't think the amount of DMT will really increase the onset. Eating 3.5g of mushrooms seems to take about the same time to kick in initially as 7+ grams ime. It's just that the total ramping feels faster since one is going deeper with a bigger dose.

250-300mg sounds a bit risky, even with experiences with high dose mushrooms. They're just not the same. I'd recommend finding an interval you feel comfortable increasing by and take several journeys increasing by that increment each time to see how it suits you.

I have not seen anything on a safe maximum dosage for DMT aside from the LD50.

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