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Tam5.2
Tamoxifen (Nolvadex) Research
Too few graded studies
955 peer-reviewed studies
What the evidence says
Too few graded studies
Tamoxifen (Nolvadex) doesn't have enough studies with structured effect-size data yet to pool a verdict. Browse the studies below for individual findings.
Most evidence is from high-quality meta-analyses and randomised trials published 1976–2026 with a typical study size of 38 participants.
Based on 954 studies · 97 meta-analyses · 831 RCTs · 38 total participants
Confidence
High confidence
By outcome
Breast cancer (treatment & prevention)
Too few graded studies714 studies
Safety profile
Too few graded studies25 studies
Gynecomastia & testosteroneBy blocking estrogen feedback, raises gonadotropins and endogenous testosterone and improves sperm parameters (off-label male use) · Weeks to a few months
Too few graded studies24 studies
Male fertilityRaises FSH/LH and improves sperm parameters — the rationale for male-infertility regimens · Weeks to a few months
Too few graded studies14 studies
Slowing down
Only 70 studies in the last 5 years · Latest meta-analysis: 2026
197620012026
1Meta-Analysis2024
In plain English: Our meta-analysis suggests that tamoxifen use may be associated with an increased PD risk in women.
Tan BBJ et al. · The American journal of the medical sciences (2024)
Using the common-effect model, the pooled OR of PD was 2.4, with (95% CI 1.91-3.01, P < 0.0001), with high heterogeneity (I2 = 81.5%, Cochran's Q test P = 0.001).
Pooling 28,640 tamoxifen-exposed patients under the common-effect model found an incidence rate of 5.86 events per 10,000 person-years (95% CI 4.82-7.12) with minimal heterogeneity (I2 = 26%, Cochran's Q test P = 0.258).
Our meta-analysis suggests that tamoxifen use may be associated with an increased PD risk in women.
In plain English: In women with breast cancer being treated with chemotherapy, the evidence is very uncertain about controlled ovarian hyperstimulation using gonadotropins plus a protective agent (letrozole or tamoxifen) compared to controlled ovarian hyperstimulation with gonadotropins in terms of the number of oocytes obtained.
Weterings MA et al. · The Cochrane database of systematic reviews (2025)
There is probably little to no difference between the use of letrozole or tamoxifen as the protective agent added to controlled ovarian hyperstimulation with gonadotropins (MD -0.04, -2.72 to 2.64; 2 studies, 203 women; I² = 0%; moderate-certainty evidence).
The evidence is very uncertain about the effect of ovarian suppression using GnRH agonists on live birth (RR 1.60, CI 0.89 to 2.87; P = 0.12; 3 studies, 599 women; I² = 0%; very low-certainty evidence).
When comparing letrozole versus tamoxifen used as the protective agent, there is probably little to no difference in the number of oocytes retrieved.