CFU is not the answer.
The first thing most probiotic labels shout at you is a number. 50 billion CFU. 100 billion CFU. The number is doing rhetorical work. It looks impressive. It is not the thing.
CFU — colony-forming units — counts live bacteria in the bottle. More bacteria is not more benefit, the way more aspirin is not more pain relief. Each clinically-studied strain has a dose range where it actually does the work it was studied to do, and that range is usually 2 to 10 billion, not 50, not 100. Past that range the strain doesn't get more effective; it just gets more expensive.
What actually matters
- Which strain. Bifidobacterium animalis subspecies lactis is a different bacterium from Lactobacillus rhamnosus. They do different jobs. The label should say genus + species. If it just says "probiotic blend," walk away.
- How much of each strain. Total CFU on the front of the bottle tells you the sum. Dose-per-strain — usually printed on the back, sometimes not at all — tells you whether any one strain is at a research-validated dose.
- What body system. Strains target a system: gut, mood, immune, metabolic. A skin-clarity strain in a "gut health" formula is filler.
How the Good Ones are dosed
Every adult Good One is the same total: 3 strains × 6 billion (Universal core) + 2 strains × 4 billion (issue-specific) = 26 billion CFU per capsule. That's enough to put each strain at its studied dose. Past that, you're paying for marketing.
The number on the front of the bottle is a sticker. The dose-per-strain on the back is the work.