At home with nothing, you and me turning to a hormone (7)
I believe the answer is:
insulin
'hormone' is the definition.
(I know that insulin is a type of hormone)
'at home with nothing you and me turning' is the wordplay.
'at home' becomes 'in' ('I'm in' can mean 'I'm at home').
'with' means one lot of letters go next to another.
'nothing' becomes 'nil' (eg nil is zero in football).
'you and me' becomes 'us'.
'turning' says the letters should be written in reverse.
'nil'+'us'='nilus'
'nilus' reversed gives 'sulin'.
'in'+'sulin'='INSULIN'
'to a' is the link.
(Other definitions for insulin that I've seen before include "Hormone substance injected by diabetics" , "Diabetes drug" , "Hormone involved in diabetes" , "Hormone: deficiency results in diabetes" , "Treatment for diabetic" .)