Erectile dysfunction is a common concern for men with type 2 diabetes, and questions often arise about whether diabetes medications contribute to this problem. Janumet, a combination of sitagliptin and metformin used to manage blood glucose levels, is not recognised as a cause of erectile dysfunction. Clinical evidence and regulatory data from the MHRA and EMA do not identify ED as an adverse effect of either component. When sexual dysfunction occurs in men taking Janumet, the underlying diabetes itself—through vascular damage, neuropathy, and hormonal changes—is typically responsible rather than the medication.

What Is Janumet and How Does It Work?

Janumet is a combination medication used to manage type 2 diabetes mellitus in adults. It contains two active ingredients: sitagliptin (a dipeptidyl peptidase-4 or DPP-4 inhibitor) and metformin (a biguanide). This dual-action formulation is prescribed when diet, exercise, and single-agent therapy do not provide adequate glycaemic control.

Sitagliptin works by inhibiting the DPP-4 enzyme, which normally breaks down incretin hormones such as glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). By blocking this enzyme, sitagliptin increases incretin levels, which in turn stimulate insulin release from the pancreas in a glucose-dependent manner and reduce glucagon secretion. This mechanism helps lower blood glucose levels. When used alone, sitagliptin has a low risk of hypoglycaemia; however, the risk increases when Janumet is combined with insulin or sulfonylureas, and dose adjustments of these other medications may be needed.

Metformin, the other component, reduces hepatic glucose production and improves insulin sensitivity in peripheral tissues, particularly muscle. It also delays intestinal glucose absorption. Metformin is considered a first-line treatment for type 2 diabetes according to NICE guidelines (NICE NG28) and has a well-established safety profile.

Janumet is typically taken twice daily with meals to reduce gastrointestinal side effects associated with metformin. Common side effects include gastrointestinal disturbances (nausea, diarrhoea), upper respiratory tract infections, and headache. Serious but rare adverse effects include lactic acidosis (associated with metformin) and pancreatitis (associated with sitagliptin). If you experience severe, persistent abdominal pain (with or without vomiting), stop taking Janumet and seek urgent medical review, as this may indicate pancreatitis.

Long-term metformin use may reduce vitamin B12 levels, which can lead to anaemia or neuropathy. Your GP may monitor your B12 levels, particularly if you are at higher risk or develop symptoms. DPP-4 inhibitors, including sitagliptin, have been associated with rare cases of bullous pemphigoid (a blistering skin condition) and severe joint pain. If you develop a new blistering rash or severe joint symptoms, contact your GP.

Regular monitoring of renal function is essential, as both components are renally excreted. Metformin is contraindicated if your estimated glomerular filtration rate (eGFR) is below 30 mL/min/1.73 m², and initiation is not generally recommended if eGFR is 30–45 mL/min/1.73 m². Dose adjustments may be required in patients with impaired kidney function. If you experience any suspected side effects, you can report them via the MHRA Yellow Card Scheme at yellowcard.mhra.gov.uk or through the Yellow Card app.

Understanding Erectile Dysfunction in Type 2 Diabetes

Erectile dysfunction (ED) is significantly more prevalent in men with type 2 diabetes compared to the general population, affecting a substantial proportion of diabetic men at some point. The relationship between diabetes and ED is multifactorial and well-established, involving vascular, neurological, hormonal, and psychological mechanisms.

Vascular complications represent the primary pathway. Chronic hyperglycaemia damages the endothelium (inner lining of blood vessels), impairing nitric oxide production—a key molecule required for penile arterial dilation and erection. Diabetes accelerates atherosclerosis, reducing blood flow to the penile arteries. Additionally, diabetes-related autonomic neuropathy can damage the nerves controlling the erectile response, further compromising function.

Hormonal factors also contribute. Men with type 2 diabetes often have lower testosterone levels (hypogonadism), which can reduce libido and erectile capacity. Obesity, commonly associated with type 2 diabetes, further suppresses testosterone production. Psychological factors, including depression, anxiety, and diabetes-related distress, compound the problem and create a cycle that perpetuates sexual dysfunction.

Regarding Janumet specifically, there is no established causal link between sitagliptin/metformin combination therapy and erectile dysfunction. Neither sitagliptin nor metformin is listed as causing ED in their Summary of Product Characteristics (SmPC) approved by the MHRA or EMA. Clinical trials and post-marketing surveillance have not identified ED as a recognised adverse effect of Janumet.

It is crucial to recognise that if ED develops or worsens during Janumet treatment, the underlying diabetes itself—rather than the medication—is the more likely cause. Poor glycaemic control, progression of diabetic complications, or other cardiovascular risk factors typically explain sexual dysfunction in this population. Any concerns should be discussed with a healthcare professional to identify the true underlying cause and appropriate management strategy.

Managing Sexual Health While Taking Janumet

Maintaining sexual health while managing type 2 diabetes requires a holistic, multidisciplinary approach that addresses both glycaemic control and the specific factors contributing to erectile dysfunction. Optimising diabetes management is foundational, as improved blood glucose control can prevent further vascular and neurological damage.

Lifestyle modifications form the cornerstone of management:

• Glycaemic control: Maintaining HbA1c within your individualised target range reduces microvascular and macrovascular complications. NICE NG28 recommends targets tailored to individual circumstances—often 48 mmol/mol (6.5%) for people on lifestyle measures or metformin alone, and 53 mmol/mol (7%) for those on medications associated with hypoglycaemia risk

• Weight management: Achieving and maintaining a healthy BMI improves insulin sensitivity, testosterone levels, and cardiovascular health

• Physical activity: Regular exercise (at least 150 minutes of moderate-intensity activity weekly) improves endothelial function, cardiovascular fitness, and psychological wellbeing

• Smoking cessation: Smoking significantly worsens vascular function and should be addressed urgently

• Alcohol moderation: Excessive alcohol consumption can impair erectile function and interfere with diabetes control

Cardiovascular risk factor management is equally important. Blood pressure control, lipid management with statins where indicated (as per NICE NG238), and antiplatelet therapy for secondary prevention (if appropriate) all contribute to preserving vascular health necessary for erectile function.

Medication review should be conducted with your GP or diabetes specialist. While Janumet itself is not implicated in causing ED, other medications commonly prescribed for diabetes-related conditions may contribute—including certain antihypertensives (some beta-blockers, thiazide diuretics), antidepressants (particularly SSRIs), antipsychotics, and 5-alpha-reductase inhibitors. Your healthcare team can assess whether alternative medications might be appropriate.

Phosphodiesterase-5 (PDE-5) inhibitors such as sildenafil, tadalafil, or vardenafil are effective first-line treatments for ED in diabetic men and can be safely prescribed alongside Janumet. Generic sildenafil is widely available on NHS prescription for men with diabetes; access to other agents may vary and some require specific criteria. These medications are contraindicated if you take nitrates (for angina) or riociguat, and caution is needed if you take alpha-blockers. Your GP will assess your cardiovascular health before prescribing. Other treatment options include vacuum erection devices, intracavernosal injections, or psychological/sexual counselling where appropriate. A comprehensive approach addressing both physical and psychological aspects typically yields the best outcomes.

When to Speak to Your GP About These Concerns

Open communication with your GP about sexual health concerns is essential, yet many men feel embarrassed or reluctant to raise these issues. It is important to recognise that erectile dysfunction is a common medical condition with effective treatments available, and your GP is accustomed to discussing these matters professionally and confidentially.

You should arrange an appointment if:

• You experience new or worsening erectile dysfunction

• Sexual problems are affecting your quality of life or relationship

• You have concerns about whether your medications might be contributing to ED

• You notice other symptoms alongside ED, such as reduced libido, fatigue, or mood changes (which might suggest low testosterone)

Seek urgent medical attention (call 999) if:

• You experience severe chest pain, breathlessness, or other symptoms suggesting a heart attack or stroke during or after sexual activity

What to expect during your consultation: Your GP will take a comprehensive medical and sexual history, including the onset, duration, and severity of symptoms. They will review your current medications, assess cardiovascular risk factors, and evaluate your diabetes control. A physical examination may be performed, and blood tests might be arranged to check testosterone levels (measured on two separate mornings to confirm any abnormality), HbA1c, lipid profile, and renal function. If testosterone is borderline, further tests such as sex hormone-binding globulin (SHBG) or free testosterone may be considered.

Your GP can provide reassurance that Janumet is not a recognised cause of erectile dysfunction and help identify the actual underlying factors. They can optimise your diabetes management, review other medications that might contribute to ED, and discuss treatment options including PDE-5 inhibitors or referral to specialist services if needed.

Referral to specialist services may be appropriate in certain circumstances, such as confirmed hormonal abnormalities requiring endocrinology input, complex or refractory cases requiring urology or andrology assessment, or psychological factors requiring psychosexual therapy. Some areas have dedicated men's health or sexual health clinics that provide specialist assessment and management.

Remember that addressing erectile dysfunction is not merely about sexual function—it often serves as an early warning sign of cardiovascular disease. Men with ED have increased risk of heart attack and stroke, making this an important opportunity to optimise overall cardiovascular health. Taking action to address these concerns benefits both sexual health and long-term wellbeing.

Frequently Asked Questions