Can Lamictal Cause Low Testosterone in Males?
Lamotrigine (Lamictal) does not cause low testosterone or hypogonadism in men and is considered weight-neutral and endocrine-neutral among antiepileptic drugs.
Evidence from Antiepileptic Drug Studies
The most comprehensive evidence comes from direct comparative studies of antiepileptic drugs and their endocrine effects:
Lamotrigine has not been shown to result in endocrine side effects, distinguishing it from enzyme-inducing antiepileptic drugs like phenobarbital, phenytoin, and carbamazepine, as well as from valproate 1.
In a controlled study of 85 men with epilepsy, bioactive testosterone levels in men taking lamotrigine were comparable to untreated controls and significantly higher than those taking carbamazepine or phenytoin 2.
Among men with epilepsy on lamotrigine, only 12% had bioactive testosterone below the control range, compared to 48% on carbamazepine and 28% on phenytoin 2.
Sexual function scores in the lamotrigine group were equivalent to controls and significantly better than enzyme-inducing antiepileptic drugs 2.
Mechanism: Why Lamotrigine Differs
The key distinction lies in lamotrigine's pharmacologic profile:
Lamotrigine does not induce liver enzymes, unlike carbamazepine and phenytoin, which increase sex hormone-binding globulin (SHBG) concentrations 1, 3.
Elevated SHBG from enzyme-inducing drugs leads to lower bioactive testosterone and estradiol over time, causing sexual dysfunction and reduced fertility 1.
Lamotrigine is classified as weight-neutral, avoiding the metabolic disruptions associated with valproate that can affect testosterone through different mechanisms 3.
Guideline Context on Drug-Induced Hypogonadism
According to the 2025 European Association of Urology guidelines on male hypogonadism, drug-induced causes include 4:
- Antiandrogens (cyproterone acetate, spironolactone, flutamide, bicalutamide)
- 5α-reductase inhibitors (finasteride, dutasteride)
- Estrogen receptor blockers
- Aromatase inhibitors
- Drugs that increase SHBG (notably anticonvulsants—but this refers specifically to enzyme-inducing agents)
Lamotrigine is conspicuously absent from these lists of medications causing hypogonadism.
Clinical Implications
If a male patient on lamotrigine presents with symptoms of low testosterone (reduced libido, erectile dysfunction, fatigue), investigate other causes rather than attributing it to the medication 5.
Common alternative explanations include obesity, metabolic syndrome, type 2 diabetes, chronic illness, opioid use, or age-related decline 4.
Switching from enzyme-inducing antiepileptic drugs to lamotrigine may actually improve testosterone levels and sexual function in men with epilepsy 2.
Important Caveat
While lamotrigine itself doesn't cause hypogonadism, epilepsy as a condition is independently associated with reproductive dysfunction in both treated and untreated patients 3, 2. In the comparative study, 20% of untreated men with epilepsy had low sexual function scores, though this was still better than those on carbamazepine (32%) or phenytoin (24%), and worse than lamotrigine (4%) 2.