I started using a hair growth tonic today. I wonder if it will work.
I started putting a tonic for hair growth in my hair today. I wonder if it will help my hair grow.
この場合、次のような言い方ができますよ。
ーI started using a hair growth tonic today. I wonder if it will work.
「今日から育毛剤を使い始めた。効くかなあ」
a hair growth tonic「育毛剤」
to work「効く」
ーI started putting a tonic for hair growth in my hair today. I wonder if it will help my hair grow.
「今日から髪に育毛剤を使い始めた。育毛の助けになるかなあ」
a tonic for hair growth「育毛剤」
ご参考まで！
カナダ 
