Weight-loss drugs and fertility: the data

A systematic review and meta-analysis published in Clinical Obesity on 17 June 2026 pooled seven clinical trials (n = 575) to examine whether weight-lowering drugs improve natural fertility in women with overweight or obesity^[1]. Six of the seven trials were randomised. The review found that orlistat was associated with higher ovulation rates than lifestyle modifications alone, and that adding semaglutide to standard treatment increased pregnancy rates compared with standard treatment alone.

Why weight and fertility are linked

Obesity disrupts the hormonal cascade that governs ovulation. Excess adipose tissue increases circulating oestrogen via aromatisation, raises insulin and androgen levels, and is a driver of anovulatory infertility. The WHO estimated in 2022 that roughly 890 million adults globally live with obesity, and a substantial proportion of those are women of reproductive age. Weight loss through diet and exercise has long been recommended as a first step for women with obesity-related subfertility, but adherence is difficult and outcomes variable. The clinical question the review addresses is whether pharmacological weight loss does anything beyond what diet and exercise achieve.

What the review found

The authors searched MEDLINE, Embase, CINAHL, CENTRAL, and ClinicalTrials.gov, screening 2,731 records down to seven eligible trials. The drugs studied were orlistat (four trials) and semaglutide (one trial); the remaining trials covered metformin or lifestyle-only comparators^[1].

For ovulation, orlistat was associated with higher ovulation rates than lifestyle modifications. When orlistat was compared head-to-head against metformin, the difference was not statistically significant (risk ratio 0.78, 95% CI 0.41 to 1.49, p = 0.45)^[1].

For pregnancy, one trial reported that orlistat improved pregnancy rates over placebo (23.3% vs 6.7%, p = 0.044). A separate trial found that adding semaglutide to standard fertility treatment increased pregnancy rates compared with standard treatment alone (35% vs 15%, p < 0.05)^[1].

Why the evidence is still thin

Seven trials and 575 participants is a small evidence base for a question this clinically important. The review itself flags this limitation. Four of the included trials studied orlistat, which is not a GLP-1 receptor agonist and acts through a completely different mechanism (gastrointestinal lipase inhibition). Only one trial tested semaglutide in a fertility context. No trials of tirzepatide, liraglutide, or any other newer weight-lowering drug met the inclusion criteria for natural fertility outcomes.

That gap matters because the drugs drawing the most clinical interest for obesity right now, including semaglutide and tirzepatide, have the thinnest fertility data. The meta-analysis is honest about this: the authors call for future research to evaluate newer weight-lowering drugs in adequately powered studies designed with fertility as a primary endpoint.

The contraception and washout question

For women who are trying to conceive, this review sits alongside a practical clinical reality: most weight-lowering drugs carry pregnancy warnings. The semaglutide prescribing label recommends discontinuation at least two months before a planned pregnancy^[2]. The NHS advises that women who could become pregnant should use contraception while on semaglutide and stop at least two months before trying to conceive^[3]. These precautions exist because animal studies showed embryofetal harm, and there is insufficient human data to establish safety in pregnancy.

The tension is real. A drug that improves ovulation and pregnancy rates may also need to be stopped before the pregnancy it helped enable. For clinicians, the question becomes one of sequencing: use the drug to achieve weight loss and ovulatory improvement, discontinue, and then attempt conception during the washout window while the metabolic benefits persist. The meta-analysis does not address that sequencing question directly, but the fertility-positive signals it reports make it more urgent.

What this does not tell us

The review measured ovulation and pregnancy rates but did not report live birth data, which is the outcome that matters most to patients. None of the seven trials were designed or powered to detect differences in live birth rates. The review also does not cover assisted reproduction (IVF or IUI); it focuses on natural fertility only.

The PCOS question is partially addressed. Several of the included trials enrolled women with polycystic ovary syndrome, a condition in which obesity-driven anovulation is a major contributor to subfertility. But the review does not stratify results by PCOS status, so it is not possible to say from this data whether the fertility benefit is specific to PCOS or applies more broadly to any obesity-related anovulation.

Where this leaves the field

The clinical takeaway is cautious. There is early evidence that pharmacological weight loss, particularly with orlistat and possibly with semaglutide, can improve ovulation and pregnancy rates in women with obesity. But the evidence comes from small trials, the drug most studied (orlistat) is not the drug most prescribed for obesity in 2026, and the one semaglutide trial is a single study. What the field needs, as the review authors state, is adequately powered trials of newer weight-lowering drugs with fertility as a primary endpoint. Until those exist, clinicians are working from signals rather than definitive evidence.