I ate a giant strength prep to no effect. Log below.
Now this is possibly by design. If so it should be noted that
I seem to remember being able to get puissance even if I am affected by giant strength. I couldn't find a log of it, so I may be imagining things.

LOG:

You finish eating a gnarled olive-green weed.
You quickly prepare a gnarled olive-green weed for proper consumption as you
place it in your mouth.
You are already as strong as you can get!


989hp 383m 835mv wilderness waning 8 PM cloudy (-23.18%) aff
You are affected by:
Skill: 'warcry' modifies save vs spell by -13 for 27 hours.
Skill: 'warcry' modifies hit roll by 7 for 27 hours.
Spell: 'detect invis' for 17 hours.
Spell: 'curse' modifies save vs spell by 12 for 8 hours.
Spell: 'curse' modifies hit roll by -6 for 8 hours.
Power: 'windwalk' for 6 hours.
Power: 'windwalk' for 6 hours.
Skill: 'berserk' modifies armor class by 25 for 4 hours.
Skill: 'berserk' modifies hit roll by 5 for 4 hours.
Skill: 'berserk' modifies damage roll by 10 for 4 hours.
Skill: 'ferocity' modifies damage roll by 6 for 4 hours.
Skill: 'puissance' modifies strength by 3 for 3 hours.
Power: 'unbound spirit' modifies morale by 10 for -1 hours.
Power: 'unbound spirit' modifies wisdom by 2 for -1 hours.

n/t