Are probiotics after a course of antibiotics genuinely useful or just marketing?

The evidence is moderate rather than overwhelming, and it is strongest for one specific outcome: reducing antibiotic-associated diarrhoea. For that, certain strains show real benefit. For the broader claim of 'restoring your gut', the picture is much weaker, and some research suggests supplements can actually slow the natural recovery of your own microbiome. Fermented foods — curd, buttermilk, idli batter, kanji — are a reasonable and cheap default. If you had significant diarrhoea on antibiotics, a targeted probiotic is worth discussing; as a routine add-on, it is mostly marketing.