Did my first "trip" this week end A++ 1.5g, but there was no trip. Had a perfect setting, sunrise at the beach, on an empty stomach.
Maybe some of my meds stuffed it. Although I did not take my anti depressants the morning.
My dealer keeps saying 1.5g is enough?
The amount of active compounds can vary wildly within a batch (were all the mushrooms from the same grow/flush, etc, not to mention the variability generally from strain to strain and within genetic lines within the same strain, etc).
My advice would be to procure at least 10 grams and grind it all into powder (to even out the distribution of the active ingredients) - From there, you can get a baseline (i.e. 1.5 grams does nothing, so as krieg said, in this case, try 3). Typically, 1 gram would be considered a threshold dose (depending on the strain, goes without saying), so unless you have something that is particularly strong it is entirely likely that 1.5 has the potential to do very little).
The important point here is to have a 'control' supply that you can test with, and titrate upwards as needed (and give it a week or so between tries).
Also recommended is to grind up the mushroom, and soak it in lemon juice for 30 minutes or so (this starts breaking down the psilocybin to psilocin, which speeds up the process).
RE medication, I have not noticed that it makes a significant difference, although it will depend what you are on; I've not noticed any significant reduction in play on various antidepressants over the years, although it is very likely that you will need a slightly higher than usual dose, compared to someone who is not on meds.
Also, be careful not to make a big jump - A strong trip, while an awesome experience, can potentially be a bit overwhelming.