The safety profile of 4-AcO-DMTs currently unknown so erowid lists a heavy dose as 25+ milligrams but there are some reports of people taking 50 milligrams without injury.
Here are some safety guidelines that I use when taking RCs.
Step 1- Identify if the compound is active at sub-milligram doses if it isn't already to rule out the possibility of mislabeled bags. If you you do not have a micro gram scale use dilution dosing use this calculator:
http://www.endmemo.com/bio/dilution.php start with 100ug and work your way up to 1 milligram. Make sure take the doses on different days because you could build tolerance
step 2- if the substance isn't active at sub-milligram try taking doses in 5mg increments until you reach the threshold dose if you get effects from the threshold dose you can proceed to take the recommended low dose. ALWAYS START WITH A LOW DOSE!!! You never know how the compound will effect you.
step 3- If all goes well you can proceed to take a medium dose then a high dose.
Tips:
NEVER EYEBALL A DOSE its like playing with fire in a room filled with explosives
http://www.erowid.org is a helpful site for dose recommendations and other info
you can all ways take more but you can never take less.
Yes this guide is a pain in the butt to do but it just may save your life. Always remember that you don't know what you are taking and even if you follow this guide I cannot guarantee your safety.
Be safe and use your head.