kick in

ＳＦのThe Martian by Andy Weirを読んでいます。
I ache all over. And the shovels I have are made for taking samples, not heavy digging. My back is killing me. I foraged in the medical supplies and found some Vicodin. I took it about ten minutes ago. Should be kicking in soon.
事故で主人公一人だけが火星に取り残され、その日誌が続き、主人公以外は余り出てこないので分かり易い話ではあります。Vicodinは痛み止めか何かの薬の様です。"kicking in" はその効き目が出てくる意味と思いますが、辞書で確認します。
・Oxford English Dictionary: (especially of a device or drug) become activated; come into effect.: I think the medication is finally kicking in and that was what I was waiting for.
・Collins Dictionary: If something kicks in, it begins to take effect.: As discounts kicked in, bookings for immediate travel rose by 15%.
・Cambridge English Dictionary: to start to have an effect or to happen: It takes half an hour for the medication to kick in.