Do Weight-Loss Injections Affect Men's Sex Lives? Erections, Sexual Desire, Testosterone and Sperm
Men losing weight with weight-loss injections, known as GLP-1 medicines, often have questions about desire, erections and fertility; because excess weight itself affects these functions, the picture is complex. What the research shows, why the penis may look bigger and when to see a doctor are covered here.
A man who starts weight-loss injections often notices in the first weeks that his appetite has dropped and his weight is falling; after a while, he may feel that his sex drive is not what it was, or that his erections have weakened. Another man describes the opposite: he feels more energetic and even says his penis has “grown”. On social media, meanwhile, conflicting information spreads quickly.
Two questions need to be separated here: how excess weight and weight loss affect sexual health, and whether the medicine itself has a direct effect. The first is well understood, whereas the evidence on the second is not yet clear. This article explains the role of excess weight, the possible effects of weight-loss injections on erections, desire, testosterone and sperm, the impression that “the penis has grown” and the risks of unregulated products.
How does excess weight affect men's sexual health?
Excess weight and obesity can affect male sexual health in several ways:
- Low testosterone: Fat tissue converts some testosterone into oestrogen; as abdominal fat increases, levels may fall.
- Erectile dysfunction: Diabetes, insulin resistance and high blood pressure accompanying excess weight can damage blood vessels and reduce blood flow to the penis.
- Sleep apnoea: Repeated pauses in breathing during sleep can contribute to tiredness and disrupted hormone balance.
- Reduced sperm quality: Obesity has been associated with lower sperm count and motility.
Weight loss can improve part of this picture, but not every complaint can be explained by weight. Because erection problems may also be an early sign of cardiovascular disease, they should be assessed in their own right.
How do weight-loss injections work?
The medicines known as weight-loss injections, GLP-1 medicines, mimic the action of certain hormones released after eating; they reduce appetite, increase the feeling of fullness, slow the emptying of the stomach and help regulate blood sugar. First used for type 2 diabetes, these prescription medicines later also came into use for weight management in people who meet certain criteria. Their most common side effects are nausea, vomiting, diarrhoea or constipation, which may be most noticeable in the first weeks.
Effect on erections: what does the evidence say?
On this most-asked question, the evidence is conflicting. The findings so far fall into three groups:
- Observational studies reporting a negative link: Some studies based on health records have reported that, among men without diabetes, erectile dysfunction was diagnosed more often in those using these medicines.
- A link that weakens with methodological adjustment: When weight, age and coexisting conditions were taken into account in more detail, this link was reported to weaken or lose significance; different medicines in the same group have also shown different results.
- Findings in a positive direction: In men with diabetes, some studies have reported improved erectile function alongside metabolic improvement.
These studies have not shown that the medicine causes erectile dysfunction, that is, a cause-and-effect relationship. Record-based studies cannot fully distinguish whether those using the medicine already carried more risk. The honest answer is that the evidence is not yet clear.
It would be wrong to set a general rule on using erectile dysfunction medicines alongside weight-loss injections; this should be discussed with the prescribing doctor, taking the man's heart condition and blood pressure into account.
Why might sexual desire decrease?
Some men say their desire has fallen since starting the medicine, while others say it has risen as they lose weight. The following are possible explanations rather than proven mechanisms:
- Low energy intake and rapid weight loss: When little food is eaten, the body may direct energy to priority functions; this can be felt as tiredness and reduced desire.
- Nausea and fluid loss: Someone experiencing nausea, vomiting, inadequate fluid intake and fatigue understandably has less interest in sex.
- Muscle loss: Without enough protein and physical activity, part of the weight lost may come from muscle; strength and energy may decline.
- Mood and a general loss of desire: Changes in mood and losing interest in other enjoyable things along with appetite can be reflected in sexual desire.
On the other hand, an improved body image and greater self-confidence have a positive effect on desire in some men, so the effect varies from person to person. Where the decrease is long-lasting, other causes of low desire should also be assessed rather than blaming the medicine alone.
Do testosterone levels change?
Low testosterone, common in men with obesity, is known to improve with weight loss. In a review of randomised controlled trials presented at an international endocrinology congress in 2026, no negative effect of these medicines on hormone levels, sexual function or sperm was seen, and testosterone was reported to rise in men with obesity. However, congress presentations are preliminary data, and studies in this area remain limited.
If complaints suggesting testosterone deficiency persist despite weight loss, assessment is made with a morning blood sample. Using testosterone without a medical assessment is not advised, as it can suppress sperm production.
Sperm quality and plans to become a father
Data on how these medicines affect sperm in men are limited; so far, no clear negative effect has been shown. Since excess weight can affect sperm quality adversely, weight loss itself may benefit sperm parameters. As sperm production follows a cycle of roughly three months, this change takes time.
There are separate recommendations about these medicines for women planning a pregnancy, and stopping the medicine before pregnancy is generally advised. For men, there is no clear guidance yet. Couples planning a child should discuss the plan with the prescribing doctor, whichever partner is using the medicine.
Where does the impression that “the penis has grown” come from?
Some men who lose weight say their penis has got bigger. The reason is the thinning of the fat pad above the pubic bone: with excess weight, the base of the penis is buried within this fat and the visible part looks shorter; as the fat decreases, this part is revealed. The actual length does not change; there is no evidence that the medicine enlarges penile tissue.
When the penis is largely hidden within fat, the condition is called buried penis; the difference between visible and actual length is explained in the “Buried Penis” and “Why Does the Penis Get Shorter?” articles on this site.
The risks of non-prescription and unregulated products
As interest has grown, “weight-loss pens” sold without a prescription through social media and the internet have become widespread. Health authorities, including the World Health Organization, have issued warnings about counterfeit versions of these medicines. The main risks of unregulated products are:
- Products of unknown content: The pen may contain none of the active substance, a different substance, or an amount different from what the label states; any complaint arising with such a product is then hard to attribute to the medicine.
- Lack of sterility: Manufacturing, storage and transport conditions are unknown, creating a risk of infection and ineffectiveness.
- Use without assessment or monitoring: These medicines are not suitable for everyone; without medical follow-up, serious side effects may be overlooked.
When should you see a doctor?
In the following situations, a discussion with the prescribing doctor and, where needed, a urology and andrology assessment are advised:
- Erection problems or a marked fall in sexual desire that begin after starting the medicine and last more than a few weeks
- Tiredness and low desire suggesting testosterone deficiency that persist despite weight loss
- Planning a child, or a pregnancy not occurring within the expected time
- Considering the use of erectile dysfunction medicines alongside weight-loss injections
- Having used a non-prescription or unregulated weight-loss product
Weight loss itself can have a positive effect on erections, sexual desire, testosterone and sperm quality in most men; the evidence on the direct effect of weight-loss injections on these functions, however, is not yet clear. If a complaint arises, rather than stopping the medicine on one's own, it should be discussed with the prescribing doctor and the underlying causes assessed. Assoc. Prof. Zülfü Sertkaya practises in urology and andrology in Istanbul; assessment and treatment planning for erection, desire and fertility concerns arising during weight loss are carried out with individual assessment and confidentiality.