In Rome I take LSD, a narcissistic act (3,4)
I believe the answer is:
ego trip
'act' is the definition.
(ego trip is a kind of act)
'in rome i take lsd a narcissistic' is the wordplay.
I cannot quite see how this works, but
'i' could be 'ego' ('I' in Latin) and 'ego' is found in the answer.
'take' could be 'r' (abbreviation for 'recipe', Latin for 'take') and 'r' is present in the answer.
The remaining letters 'tip' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for ego trip that I've seen before include "Action to inflate one's sense of self-importance" , "Act of self-aggrandisement" , "Bout of boosting self-esteem" , "Something done to boost self-importance" , "Self-gratifying experience" .)