Benefits
Male lower urinary symptoms (LUTS) eased in a dose-response trial
In a 6-month double-blind trial of 124 men over 45 with urinary symptoms and PSA below 2.5 ng/mL, the IPSS symptom score fell by 4.1 points on 500 mg/day and 3.1 on 250 mg/day, versus 1.5 on placebo. Urine flow, residual urine and bladder volume improved on 500 mg compared with starting values. Two Naturex scientists co-authored it, and it has not been repeated independently.
Urination frequency and urgency in women
In a 24-week double-blind trial funded by Naturex, 98 women with dry overactive bladder took 500 mg/day of a Naturex cranberry powder that the company identifies as Flowens, or placebo. In the 60 women analyzed per protocol, daily urinations fell by about 1.9 and urgency episodes by about 2.8 versus placebo, but the intent-to-treat analysis showed no significant difference.
Urinary tract health in women (cranberry products as a group)
A 2023 review of 50 trials of many different cranberry products found about 30% fewer symptomatic, culture-confirmed urinary tract infections with cranberry (moderate certainty), including in women with recurrent infections, but little or no benefit in pregnancy or in elderly care-home residents. None of these trials tested Flowens specifically.
Urinary flow and symptom scores in an earlier men's trial
In an earlier 6-month trial by several of the same researchers, 42 men with urinary symptoms, raised PSA, a negative prostate biopsy and non-bacterial prostate inflammation took 1,500 mg/day of dried cranberry powder or nothing. Symptom scores, quality of life, urine flow and total PSA improved only with cranberry. There was no placebo, and the powder was not identified as Flowens.
Mechanism of action
A-type proanthocyanidins and bacterial adhesion
Cranberry contains A-type proanthocyanidins (PACs), which in lab studies stop P-fimbriated E. coli from sticking to the cells lining the bladder, as summarized in the 2023 Cochrane review. This is the usual explanation for cranberry research on urinary tract infections; it does not explain the symptom-score results in the Flowens trials.
Urinary symptom effects: mechanism unknown
How cranberry might ease urinary symptoms in men or women is not known. The Flowens trials measured symptoms, urine flow and blood markers, not bladder or prostate mechanisms, and the earlier men's trial found no change in CRP or testosterone.
Whole-fruit powder rather than a purified extract
Flowens is a whole dried cranberry fruit powder rather than a purified PAC extract, so it also contains the fruit's other natural compounds, such as organic acids, flavonols and anthocyanins. No study has compared it with a purified PAC extract for urinary symptoms, so whether the whole fruit matters is untested.
Clinical trials
Randomized, double-blind, placebo-controlled trial of 250 or 500 mg/day Flowens for 6 months; primary outcome IPSS at 3 and 6 months; two authors were Naturex scientists (Vidlar et al. 2016, World J Urol)
124 men over 45 with PSA below 2.5 ng/mL and an IPSS of 8 or more, studied at Palacky University, Olomouc, Czech Republic.
IPSS fell by 4.1 points on 500 mg (p<0.001) and 3.1 on 250 mg (p=0.05), versus 1.5 on placebo, with a dose-response. Maximum and average urine flow, post-void residual volume and bladder volume improved on 500 mg compared with baseline. There was no effect on clinical chemistry or blood counts.
Randomized, double-blind, placebo-controlled 24-week trial of 500 mg/day dried cranberry powder versus a maltodextrin placebo, funded by Naturex-DBS (Cho et al. 2021, J Urol)
98 women aged 18 or older with dry overactive bladder; 77 completed all visits and 60 were analyzed per protocol.
Per protocol, daily urinations fell by 1.91, urgency episodes by 2.81 and bladder-condition scores by 0.66 versus placebo. Nocturia, volume per urination and the other questionnaires did not differ. In the intent-to-treat analysis, the differences in urinations (1.04, p=0.20) and urgency episodes (1.46, p=0.08) were not significant.
Randomized controlled 6-month trial of 1,500 mg/day dried cranberry powder versus no treatment, not placebo (Vidlar et al. 2010, Br J Nutr)
42 men with lower urinary tract symptoms, raised PSA, a negative prostate biopsy and chronic non-bacterial prostatitis (21 per group).
IPSS, quality of life, urine flow measures, post-void residual volume and total PSA improved in the cranberry group only; testosterone and CRP did not change. With an untreated control and no placebo, expectation effects cannot be ruled out, and the powder was not identified as Flowens.
Systematic review and meta-analysis of 50 randomized trials of many cranberry products (Williams et al. 2023, Cochrane Database Syst Rev)
8,857 randomized participants; 6,211 in the main analysis of symptomatic, culture-verified infections.
Cranberry products reduced symptomatic, culture-verified urinary tract infections (RR 0.70, 95% CI 0.58 to 0.84, moderate certainty), including in women with recurrent infections (RR 0.74), children and people after urinary procedures, with little or no benefit in elderly institutionalized people, pregnant women or people with bladder-emptying problems. Not specific to Flowens.