A tart berry studied mainly for preventing repeat bladder and urinary infections by keeping bacteria from sticking to the urinary tract. Best-supported benefit is in women who get them often, children, and people made prone by a medical procedure, and it depends on a high enough dose. Other proposed benefits are weaker or unproven. (Full Review)

Protocol

Standard preventive dose

≥36 mg proanthocyanidins daily

Commonly 500 mg whole-cranberry powder capsule once daily, or 240–300 mL unsweetened juice once or twice daily

Form

Standardized capsules or powder

Preferred over sweetened juice; standardized to A-type proanthocyanidins by the validated BL-DMAC method

Timing

Evening, consistent daily

Evening sometimes preferred for overnight urinary coverage; split twice-daily dosing may maintain more continuous coverage

Time to effect

Reduced recurrent infections

Weeks to months

Trials showing benefit typically ran 12–24 weeks

Urinary anti-adhesion activity

Within hours

Measurable for roughly 8–12 hours after a dose

Benefits

High: Prevention of recurrent urinary tract infections

Medium: Modest reduction in systolic blood pressure

Low: Improvement in blood lipid profile; support for Helicobacter pylori eradication

Speculative: Favorable shifts in the gut microbiome; cognitive and stress-resilience effects

Contraindications

History of calcium-oxalate kidney stones

Known cranberry allergy

Key Interactions

Warfarin (vitamin K antagonist anticoagulant)

Other anticoagulants and antiplatelets (aspirin, clopidogrel)

CYP2C9 / CYP3A4 substrate drugs (statins such as atorvastatin, nifedipine, some NSAIDs such as ibuprofen)

Risk & Side Effects

High: Gastrointestinal upset

Medium: Increased bleeding risk with warfarin

Low: Increased risk of calcium-oxalate kidney stones

Speculative: Interactions affecting other metabolized drugs; excess sugar and caloric load from juice

Monitoring

Marker	Target	Why
Urine culture	No significant growth (<10³ CFU/mL)	Confirms presence/absence of infection
Urinalysis (leukocyte esterase, nitrites)	Negative	Screens for white blood cells and bacteria suggesting infection
Systolic / diastolic blood pressure	<120 / <80 mmHg	Tracks the modest cardiovascular signal
HDL cholesterol	>60 mg/dL	Monitors the lipid measure most likely to shift
Urinary oxalate (if stone history)	<40 mg/24 h	Flags oxalate load relevant to stone risk

Cadence: Urine cultures at symptom onset and at ~3 and 6 months; blood pressure and lipid panel at baseline and after ~8–12 weeks

Qualitative Assessment

Reduced frequency and severity of urinary symptoms (urgency, burning, frequency)
Longer interval between infection episodes
General gastrointestinal tolerance (absence of upset or reflux)
Subjective sense of fewer "flare" periods over a season

Cranberry for Health & Longevity

Protocol

Benefits

Risk & Side Effects

Monitoring

Qualitative Assessment