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Pro-viron – patient leaflet, side effects, dosage

Last updated: · Text from the MHRA, as of · About this document

Medicine status: Controlled drug (Schedule 4) No longer supplied Details

Medicine strength:
25 mg
Contains active substance:
ATC code:

Sources: Original (products.mhra.gov.uk) · About this document

Patient leaflet - Pro-viron

1. What Pro-Viron is and what it is used for What is Pro-Viron?

Pro-Viron is a medicine containing mesterolone. It is a form of androgen (male hormone) therapy.

What is Pro-Viron used for?

R Pro-Viron is used in men who do not naturally

produce enough androgens (male hormones). R It is also used in men who are infertile due to

low levels of male hormones (caused by hypogonadism, inadequate functioning of the testes).

2. Before you take Pro-Viron

Do not take Pro-Viron if:

R you are allergic (hypersensitive) to mesterolone

or any of the other ingredients of Pro-Viron (see Section 6: Further Information)

R you have prostate cancer

R you have (or have had) a liver tumour.

Take special care with Pro-Viron:

R You will have regular examinations of the

prostate while taking Pro-Viron to rule out the possibility of prostate cancer. This is because Pro-Viron may increase the growth rate of this type of cancer.

R Using hormones, such as the one in Pro-Viron, has rarely been linked to benign

(non-malignant) liver tumours. Very rarely, using hormones has been associated with some forms of liver cancer (malignant liver tumours). Liver tumours may lead to bleeding in the abdomen, which can be life-threatening. If you have any new “stomach” discomfort or pain that does not go away quickly, you must tell your doctor straight away.

R Pro-Viron is not suitable for body-building, increasing muscles in healthy men or for increasing other physical ability.

R Pro-Viron should be taken by men only. Taking or using other medicines

Please tell your doctor if you are taking or have recently taken any other medicines, including medicines obtained without a prescription. Driving and using machines

Taking Pro-Viron is not thought to have any effect on driving or using machines.

Important information about some of the ingredients in Pro-Viron

R If you have been told by your doctor that you cannot tolerate or digest some sugars, tell your doctor before you start taking Pro-Viron. This is because it contains lactose (a type of sugar). R Pro-Viron contains methyl and propyl parabens which may cause allergic reactions (possibly delayed).

Package Leaflet: Information for the user

Pro-Viron®

25mg tablet

Mesterolone

1.3.2 1

85993526

This area must be identical on both sides!

3. How to take Pro-Viron

Always take Pro-Viron exactly as your doctor has

told you. Ask your doctor or pharmacist if you are

not sure.

RThe usual amount is one tablet, taken 3 or 4

times a day.

RSwallow the tablet whole with a drink of water.

After you have taken Pro-Viron for a few months,

your doctor may decide to reduce the number of

tablets you need to take each day.

If you take more Pro-Viron than you should

Talk to your doctor who will tell you what you need

to do. There have been no reports of serious illness

from taking too much Pro-Viron.

If you forget to take Pro-Viron

Do not take a double dose to make up for a

forgotten tablet. When you remember, take the next

dose and continue with the tablets as normal.

If you have any further questions on the use of this

product, ask your doctor or pharmacist.

4. Possible side effects

Like all medicines, Pro-Viron can cause side effects,

although not everybody gets them.

RDiscomfort or pain in your “stomach”

(abdomen)

If you get pain or discomfort in your “stomach” or

abdomen that does not go away quickly, tell your doctor straight away. (See Section 2: Before you

take Pro-Viron).

RFrequent erections or erections that do not go

away

If you get unusually frequent erections or erections

that do not easily go away, tell your doctor. Your

doctor may ask you to stop taking Pro-Viron in

order to avoid injury to your penis.

Talk to your doctor if you notice any change in

your health or general sense of well-being when

taking Pro-Viron.

Reporting of side effects

If you get any side effects, talk to your doctor. This

includes any possible side effects not listed in this

leaflet. You can also report side effects directly via

the Yellow Card Scheme at: www.mhra.gov.uk/

yellowcard. By reporting side effects you can help

provide more information on the safety of this

medicine.

5. How to store Pro-Viron

RKeep this medicine out of the sight and reach of

children.

RDo not use Pro-Viron after the expiry date which

is stated on the box after the letters ‘EXP’. The

expiry date refers to the last day of that month.

RMedicines should not be disposed of via

wastewater or household waste. Ask your

pharmacist how to dispose of medicines no

longer required. These measures will help to

protect the environment.

6. Further Information

What Pro-Viron contains

RThe active substance is mesterolone.

Each tablet contains 25mg of mesterolone.

RThe other ingredients are lactose, maize starch,

povidone (E1201), methylparaben (E218),

propylparaben (E216) and magnesium stearate

(E572).

What Pro-Viron looks like and contents of the

pack

Each pack of Pro-Viron contains 3 strips of 10 white

tablets.

Marketing Authorisation Holder and

Manufacturer

Marketing Authorisation Holder:

Bayer plc

400 South Oak Way,

Reading, RG2 6AD

United Kingdom

Manufacturer:

Bayer AG

Berlin

Germany

or

Bayer Weimar GmbH &Co KG

Weimar

Germany

This leaflet was last revised: August 2017

1.3.2 2

About this document

Source: MHRA - Medicines and Healthcare products Regulatory Agency (products.mhra.gov.uk) · Marketing authorisation: PL 00010/0562

Last revision stated in the text: August 2017 · MHRA data as of 13 October 2026

Found a mistake? Tell us on the contact page.

The information on this site does not replace the advice of a doctor or pharmacist.

Facts about Pro-viron

Controlled drug
Yes, Schedule 4 of the Misuse of Drugs Regulations?
  • Controlled drugs are medicines that UK law controls more strictly because they can be misused or cause dependence. The Misuse of Drugs Regulations 2001 divide them into 5 schedules: schedule 1 has the strictest rules, schedule 5 the lightest.
  • Schedule 4 has lighter rules. Its part II covers anabolic steroids and hormones such as growth hormone.
  • A prescription is valid for 28 days and usually covers up to 30 days of treatment.
  • Travelling abroad: you can usually carry up to 3 months' supply. Take your prescription or a letter from your doctor to show it is yours, and check the rules of the country you are going to (GOV.UK).
  • Never give it to anyone else.
Active substance Mesterolone
Strength 25 mg
Pharmaceutical form Oral tablet
How is it taken Oral
Excipients Lactose, maize starch, povidone 25 000 (E1201), methyl parahydroxybenzoate (E218), propyl parahydroxybenzoate (E216), magnesium stearate (E572)
Is it available? No, all its packs are listed as discontinued (NHS Dictionary of Medicines and Devices – not a record of current supplies)
Shelf life 5 years.
Storage None
Drug group (ATC)
  1. G Genito urinary system and sex hormones
    1. G03 Sex hormones and modulators of the genital system
      1. G03B Androgens
        1. G03BB 5-androstanon (3) derivatives
          1. G03BB01 mesterolone
Marketing authorisation PL 00010/0562 (first authorised 1 May 2008)
Marketing authorisation holder Bayer plc
Codes BNF 06040200

Sources: the MHRA product information (products.mhra.gov.uk) and the NHS Dictionary of Medicines and Devices (dm+d), release 10.2.0 of 19 October 2026, NHS Business Services Authority. Contains public sector information licensed under the Open Government Licence v3.0.