They give such 'injections' in the ear that one must now give up cigarettes and alcohol.

This couplet uses a clever image: 'injections in the ear.' It's not about actual needles, but about someone giving such powerful and persuasive advice that it feels like it's directly injected into your mind. The advice is clear and vital: 'now leave cigarettes and alcohol.' It highlights how effective and perhaps persistent a well-wisher's words can be in urging us to give up harmful habits. It’s about someone caring enough to gently but firmly guide us towards a healthier life, almost as if their words are a potent remedy for our well-being.