The relevant framing is that risk here comes from three separate places: what the material is, how it is handled, and what it does. They need three different mitigations.
Material risk is reduced by independent testing: identity, purity and quantified content on your own lot, before committing to a larger order. That is the only step that addresses what is actually in the vial.
Have a plan for stopping before you start, including what you would do with the remaining material and how you would tell someone what you had taken.
Withheld information is a recognised barrier to effective clinical assessment, and disclosure changes management in a substantial fraction of cases.
Learn the handful of symptoms that end the discussion and start a clinical one.