I love mushrooms but the nausea was ruining the come-up of every trip. Over about ten experiences, I systematically tested every anti-nausea strategy I could find. Here's what actually worked.
What didn't help much: eating ginger candy during the trip (too late by then), taking Pepto-Bismol (minor help), eating mushrooms on a full stomach (made it worse and delayed onset).
What helped somewhat: fasting for 4-6 hours before dosing, fresh ginger tea 30 minutes before eating the mushrooms, taking 25mg diphenhydramine (Dramamine) 1 hour before.
What works well: making tea instead of eating raw material. Simmer ground mushrooms in water with ginger for 15 minutes, strain out the solids, drink the liquid. The chitin in mushroom cell walls is what causes most of the GI distress, and you don't need to ingest it. You lose maybe 10-15% potency but eliminate 80% of nausea.
What works best: lemon tek + straining. Soak powdered mushrooms in lemon juice for 20 minutes, then strain through a coffee filter. Drink only the liquid. Virtually zero nausea and a faster, more intense onset. This is now my standard preparation.
Bonus tip: lying down during the come-up helps significantly. Movement and standing during the first 30-45 minutes makes nausea worse. Set up your space so everything you need is within arm's reach before dosing.