Does Semaglutide Affect Testosterone Levels?

You've started semaglutide and your energy has shifted, is your testosterone changing?

It's a question our prescribers hear fairly often, usually from men who notice they feel more alert or less fatigued a few months into treatment, and want to know whether the medicine is doing something hormonal. The honest answer is: not directly. Semaglutide is a GLP-1 receptor agonist, it works primarily on appetite signalling and gastric emptying. There is no receptor interaction with the testes, ovaries, or the hypothalamic-pituitary axis that would directly raise or suppress testosterone.

What does happen is that carrying significant excess weight suppresses testosterone in men. Adipose tissue converts androgens to oestrogens via an enzyme called aromatase; the more body fat, the more conversion, and the lower free testosterone tends to sit. Shed that fat and the aromatase activity falls. Several studies have shown that weight loss of around 10% or more is associated with meaningful rises in both free and total testosterone, independently of how the weight was lost. Semaglutide, by producing that weight loss, creates the conditions for that hormonal shift. The medicine is the vehicle; the weight change is the mechanism.

The STEP 1 trial (68 weeks, roughly 1,900 adults with obesity) documented average weight loss of around 15% at the 2.4 mg dose, published in the New England Journal of Medicine. That scale of weight reduction is exactly the range where testosterone changes become clinically observable in men.

What about women, PCOS, and androgen balance?

For women, the picture is different and the question is usually the reverse: elevated androgens rather than low ones. Polycystic ovary syndrome is the most common androgen-excess condition in women of reproductive age, and obesity worsens it, insulin resistance drives androgen production, and excess weight amplifies that cycle. GLP-1 medicines improve insulin sensitivity and reduce weight, both of which tend to lower androgen levels in women with PCOS.

Early research and clinical observation suggest that women with PCOS may see improvements in androgen-related symptoms (irregular cycles, hirsutism) as weight falls on semaglutide. The evidence base is still growing, and no large randomised trial has been designed specifically around PCOS and semaglutide at the time of writing. That means clinicians are drawing on mechanism-level reasoning and smaller studies, not a definitive answer. If PCOS or androgen balance is part of your picture, it is worth flagging explicitly at consultation so it informs the prescribing decision.

Worth noting: semaglutide's effects on blood sugar regulation feed into this too, since insulin resistance and androgen excess are tightly linked in PCOS. Improvements in one tend to move the other.

Should you monitor hormone levels while on semaglutide?

Routine testosterone monitoring is not a standard part of semaglutide prescribing in the UK, the NHS patient information for semaglutide does not list testosterone changes as a side effect to monitor. However, if you already have a diagnosed hormonal condition (hypogonadism, PCOS, or you're on testosterone replacement therapy) your prescriber needs that information before treatment starts, not as an afterthought.

There is also a practical interaction worth knowing about. Some men on testosterone replacement therapy use injectable formulations, while others use topical gels or oral preparations. Semaglutide slows gastric emptying, which can affect oral medication absorption; if you are taking any oral hormonal treatment, raise that with your prescriber. For a fuller picture of how semaglutide interacts with blood results more broadly, our page on semaglutide and blood work covers what to expect from routine monitoring.

If you're curious whether taking semaglutide and testosterone replacement at the same time raises any specific concerns, that topic has its own dedicated page: can you take semaglutide and testosterone together.

The sleep connection, energy, and what's actually driving any changes you feel

Men with obesity and low testosterone often have obstructive sleep apnoea. Weight loss improves sleep apnoea, sleep quality improves, and with it energy, mood, and libido, all of which people sometimes attribute to a testosterone surge. Some of it may be hormonal. A lot of it is simply sleeping properly again.

Semaglutide's effects on energy and mood are sometimes noticeable within the first few weeks, well before significant weight has come off. That early shift is more likely to reflect reduced food noise and better metabolic signalling than any hormonal change. Our page on semaglutide and sleep looks at this in more detail.

The bottom line is straightforward. Semaglutide does not suppress testosterone, nor does it directly boost it. If your levels change, weight loss is the most plausible explanation, and that is usually good news. If hormone health is a specific concern for you, it belongs in your consultation. At nume, a GPhC-registered prescriber reads every consultation personally on the day it arrives. If you'd like to explore whether Lilly's version of semaglutide or another formulation is right for you, start your free consultation and put your full medical picture in front of a real clinician.