Proviron or Anastrozole: What Is the Difference

Proviron (mesterolone) and anastrozole are often mentioned together in conversations about "estrogen control." However, these are drugs from completely different pharmacological groups: the first is an androgen, a derivative of dihydrotestosterone; the second is a non-steroidal aromatase inhibitor created for the treatment of breast cancer. The editorial team explains how they differ and why substituting one for the other is faulty logic.

Why these drugs are compared at all

In the sports community, there is a widespread notion that both drugs "remove estrogen." It is on this shared myth that the question "which of them is better" arises. To answer it, one must first clearly separate their mechanisms.

Anastrozole does indeed lower estradiol levels: it blocks the enzyme aromatase, which converts androgens into estrogens. This is a documented and measurable effect, on which its oncological use is based.

Proviron does not block aromatase. It is an androgen that does not itself convert to estradiol. Any assumptions about its "anti-estrogenic" action in humans are based mostly on theoretical considerations and anecdotal observations, not on clinical trials.

Thus, these drugs are compared not because they are similar, but because they are credited with a similar result. In reality, one adds yet another androgen to the body, while the other changes the balance between androgens and estrogens.

Proviron: a DHT-based androgen

Mesterolone is 1α-methyl-dihydrotestosterone. The methyl group at position 1α makes it possible to take it orally, while the drug is not 17α-alkylated, so its hepatotoxicity, according to reviews, is lower than that of classic oral steroids.

As a DHT derivative, mesterolone does not aromatize and has a predominantly androgenic rather than anabolic effect. It suppresses gonadotropin secretion more weakly than many other androgens in comparable amounts, but it is not entirely free of this effect.

In some countries mesterolone is registered for the treatment of androgen deficiency and fertility disorders associated with hypogonadism. At the same time, a multicenter placebo-controlled WHO study (1989) found no benefit of mesterolone in idiopathic male infertility.

In the WADA Prohibited List, mesterolone is included in section S1 "Anabolic agents" and is prohibited at all times.

Anastrozole: an aromatase inhibitor

Anastrozole is a non-steroidal triazole third-generation aromatase inhibitor. According to the Arimidex label, it is indicated for adjuvant therapy and treatment of hormone-receptor-positive breast cancer in postmenopausal women; in medical practice the drug is taken daily at a dose of 1 mg specified in the label.

The effectiveness of anastrozole has been proven in large randomized trials, the most well-known of which is ATAC (Baum et al., 2002), where anastrozole was compared with tamoxifen in women with early breast cancer.

In men anastrozole has no registered indications. It was studied, for example, in older men with low testosterone: aromatase inhibition raised testosterone, but in the study by Burnett-Bowie and colleagues (2009) it was accompanied by a decrease in bone mineral density of the spine compared with placebo.

WADA classifies aromatase inhibitors in section S4 "Hormone and metabolic modulators"; they are prohibited at all times, both in and out of competition.

Mechanisms: where exactly each one acts

The diagram below shows the fundamental difference. Testosterone in the body has two main pathways of conversion: to DHT via 5α-reductase and to estradiol via aromatase. Anastrozole blocks the second pathway. Proviron does not affect any enzyme, but is itself a ready-made molecule similar to DHT.

It follows that the effects of these drugs are not interchangeable. Proviron adds an androgenic load, while anastrozole changes the hormonal balance, reducing estradiol in all tissues, including bones, brain, and blood vessels.

It also matters that neither drug "protects" against the consequences of supraphysiological doses of androgens - decreased HDL, erythrocytosis, suppression of the hormonal axis.

Risks and the role of estradiol in men

Estradiol in men is not a "superfluous" hormone. A study by Finkelstein and colleagues (2013) in the New England Journal of Medicine showed that it is precisely estrogen deficiency in men that is responsible for the accumulation of fat tissue, and also affects sexual function. Excessive suppression of estradiol can reduce libido, worsen the lipid profile, and harm bone condition.

For anastrozole the label describes side effects such as joint pain, hot flashes, decreased bone mineral density, and increased cholesterol. In postmenopausal women these are known class effects of aromatase inhibitors.

For mesterolone the risks are typical of androgens: acne, acceleration of androgenic hair loss in predisposed people, effect on the prostate, suppression of spermatogenesis, and, in women, virilization.

• An independent "reduction of estrogen" without an estradiol test is treating an indicator that no one measured.
• The consequences of excessive suppression of estradiol are joint pain, fatigue, decreased libido, and loss of bone mass.
• Gynecomastia and other complaints require examination by a doctor, because they can have various causes, including tumors and liver diseases.

Editorial conclusions

Proviron and anastrozole belong to different pharmacological groups: the first is a DHT-based androgen, the second is an aromatase inhibitor. They are not interchangeable and have different indications, different targets, and different risk profiles.

The notion that both "remove estrogen" has no reliable clinical confirmation for proviron, and for anastrozole it ignores the important role of estradiol in the male body.

Any questions related to estrogens, gynecomastia, or fertility are resolved by an endocrinologist or andrologist on the basis of tests.

The editorial team also recommends the materials "Proviron vs Anastrozole: what to choose and for whom," about the role of estradiol in men, and about the causes of gynecomastia.

References

1. Finkelstein JS, Lee H, Burnett-Bowie SA, et al. Gonadal steroids and body composition, strength, and sexual function in men. N Engl J Med. 2013;369(11):1011–1022.
2. Burnett-Bowie SA, McKay EA, Lee H, Leder BZ. Effects of aromatase inhibition on bone mineral density and bone turnover in older men with low testosterone levels. J Clin Endocrinol Metab. 2009;94(12):4785–4792.
3. Baum M, Budzar AU, Cuzick J, et al. Anastrozole alone or in combination with tamoxifen versus tamoxifen alone for adjuvant treatment of postmenopausal women with early breast cancer: first results of the ATAC randomised trial. Lancet. 2002;359(9324):2131–2139.
4. Arimidex (anastrozole) tablets. Prescribing information. AstraZeneca; U.S. Food and Drug Administration.
5. World Health Organization Task Force on the Diagnosis and Treatment of Infertility. Mesterolone and idiopathic male infertility: a double-blind study. Int J Androl. 1989;12(4):254–264.
6. Kicman AT. Pharmacology of anabolic steroids. Br J Pharmacol. 2008;154(3):502–521.
7. World Anti-Doping Agency. International Standard: Prohibited List. Montreal: WADA; 2025.