Enclomiphene and the Liver

Enclomiphene is often marketed as a «clean» and «gentle» drug, including for the liver. This claim rests partly on real data and partly on assumptions. The editorial team examined what is known about the hepatic metabolism of enclomiphene, what safety signals clinical studies recorded, and where our knowledge ends.

Metabolism: From Pill to Excretion

Enclomiphene is taken orally, and after absorption in the intestine it first passes through the liver. Like clomiphene in general, it is metabolized mainly by enzymes of the cytochrome P450 system, primarily CYP2D6, as well as other isoenzymes. This produces hydroxylated metabolites, some of which have high affinity for estrogen receptors.

The key pharmacokinetic difference from clomiphene concerns the duration of stay in the body. Enclomiphene is eliminated much faster than the cis-isomer zuclomiphene: its half-life is measured in hours, whereas zuclomiphene can remain in the blood for weeks. It was precisely the absence of zuclomiphene accumulation that the developers considered the main advantage of the pure isomer.

The main route of elimination of clomiphene and its metabolites is via bile and feces. For enclomiphene, as part of the same molecular family, a similar route can logically be expected, although detailed data on the elimination of the pure isomer specifically have been published in a smaller volume than for clomiphene.

For the liver, a shorter half-life means less prolonged exposure for the same number of doses. However, this does not negate the fact that all the work of metabolizing the drug falls precisely on the liver, so its functional state directly affects the concentration of enclomiphene in the blood.

Enzyme Genetics and Drug Interactions

The CYP2D6 enzyme is known for significant genetic variability. In the population there are people with very slow, normal, and ultrarapid metabolism via this enzyme. For clomiphene, pharmacogenetic studies have shown that the CYP2D6 genotype affects the formation of active metabolites and, probably, the response to treatment.

For enclomiphene there are few targeted pharmacogenetic studies, but since it is the main substrate of this pathway within clomiphene, similar variability is quite likely. In practice, this means that the same amount of the drug in different people can produce different concentrations of the substance and its metabolites.

Even more important are interactions with other drugs. A number of common medications inhibit CYP2D6: some antidepressants (fluoxetine, paroxetine), bupropion, certain antiarrhythmic agents. Taking them at the same time could theoretically alter the metabolism of enclomiphene. That is exactly why the doctor should know about all the medications and supplements the patient takes.

In the sporting environment, an additional factor is the combination of several substances at once — from oral steroids to fat burners and alcohol. Each of them burdens the liver in its own way, and it is impossible to predict the total effect of such a «cocktail».

• The CYP2D6 genotype affects the metabolism of clomiphene and, probably, enclomiphene.
• CYP2D6 inhibitors can alter the concentration of the drug.
• Simultaneous intake of hepatotoxic substances complicates risk assessment.

What Clinical Studies Showed

In phase II and III studies published by Kaminetsky (2013), Wiehle (2014), and Kim (2016), enclomiphene was taken by men with secondary hypogonadism over several months. The authors did not report clinically significant signals of liver toxicity; the overall tolerability profile was described as acceptable.

At the same time, it is worth understanding the limitations of these data. The studies lasted months, not years, included a limited number of participants, and excluded people with active liver diseases. Rare idiosyncratic reactions that occur at a frequency of one case per thousands of patients simply cannot be detected in such samples.

The absence of registration also means that enclomiphene has no post-marketing surveillance systems, unlike registered drugs. It is precisely post-registration reports that often reveal rare liver reactions. For clomiphene, for example, the LiverTox database lists isolated cases of cholestatic injury, known specifically from many years of practice.

So the correct wording sounds like this: in short-term clinical studies no signals of hepatotoxicity were detected, but there are insufficient data to conclude about safety with long-term use or in people with liver diseases.

Enclomiphene, Clomiphene, and Oral Steroids

Enclomiphene is a non-steroidal compound, and it lacks the 17-alpha-alkyl group responsible for the classic hepatotoxicity of oral anabolic steroids. Therefore it is incorrect to put it on par with methandienone or stanozolol in terms of the effect on the liver.

Compared with clomiphene, enclomiphene theoretically has an advantage in the form of faster elimination and the absence of zuclomiphene accumulation. However, clomiphene is contraindicated in liver diseases, and there are no data that would allow this restriction to be lifted for the pure isomer. It is logical to apply the same caution.

Also indirectly related to the liver is the effect on the proteins it synthesizes. Estrogen receptor modulators can raise sex hormone-binding globulin and alter the lipid profile. These are not signs of liver damage, but they indicate that the drug affects its synthetic function.

The biggest «liver» risk of enclomiphene from the illegal market is associated not with the molecule itself but with possible substitution. Under the name of enclomiphene, clomiphene, another substance, or a product with impurities may be sold, and then all the calculations counting on a «pure isomer» lose their meaning.

Practical Monitoring and the Limits of Knowledge

If a doctor decides to use enclomiphene off-label, it is reasonable to take into account the same principles as for clomiphene. Before starting, they assess the history of liver diseases, alcohol consumption, other drugs, and, when indicated, biochemical liver tests: ALT, AST, GGT, alkaline phosphatase, bilirubin.

During treatment, tests are repeated according to clinical indications, especially if the person has risk factors or is simultaneously taking other drugs that affect the liver. For people who train intensively, it is worth remembering the effect of exercise on AST and ALT and, if needed, adding creatine kinase.

Alarming symptoms are jaundice, itching, dark urine, light-colored stool, pain in the right hypochondrium, and marked weakness. Their appearance requires immediate cessation of use and consultation with a doctor — regardless of how «safe» the drug is considered.

The honest position is that our knowledge of the effect of enclomiphene on the liver is limited to short-term studies in selected participants. This does not mean the drug is dangerous, but neither does it give grounds to call it proven safe.

Editorial Conclusions

Enclomiphene is metabolized in the liver, mainly with the participation of CYP2D6, and is eliminated faster than clomiphene because it does not contain zuclomiphene.

In short-term phase II–III studies no signals of hepatotoxicity were recorded, but there are no long-term data or studies in people with liver diseases.

Enzyme genetics, drug interactions, and the dubious quality of products from the illegal market may matter more than the properties of the molecule itself.

We also recommend reading «Clomiphene and the Liver», «The History of Enclomiphene», and «Tests When Using Clomiphene».

References

1. Kaminetsky J, Werner M, Fontenot G, Wiehle RD. Oral enclomiphene citrate stimulates the endogenous production of testosterone and sperm counts in men with low testosterone: comparison with testosterone gel. J Sex Med. 2013;10(6):1628–1635.
2. Wiehle RD, Fontenot GK, Wike J, et al. Enclomiphene citrate stimulates testosterone production while preventing oligospermia: a randomized phase II clinical trial comparing topical testosterone. Fertil Steril. 2014;102(3):720–727.
3. Kim ED, McCullough A, Kaminetsky J. Oral enclomiphene citrate raises testosterone and preserves sperm counts in obese hypogonadal men, unlike testosterone gel: results from two phase III trials. BJU Int. 2016;117(4):677–685.
4. Hill S, Arutchelvam V, Quinton R. Enclomiphene, an estrogen receptor antagonist for the treatment of testosterone deficiency in men. IDrugs. 2009;12(2):109–119.
5. LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. Clomiphene. Bethesda (MD): National Institute of Diabetes and Digestive and Kidney Diseases; 2012–.
6. U.S. Food and Drug Administration. Clomid (clomiphene citrate tablets USP): prescribing information.