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Last Updated on eMC 09-Oct-2017 View changes  | Bayer plc Contact details

The Patient Information Leaflet (PIL) is the leaflet included in the pack with a medicine. It is written for patients and gives information about taking or using a medicine. It is possible that the leaflet in your medicine pack may differ from this version because it may have been updated since your medicine was packaged.

Please click on the link to the left to view the PIL in PDF format.

Text only version for the visually impaired
Below is a text only representation of the Patient Information leaflet. The original may contain images or tables and can be viewed in PDF format using the link to the left. This PIL may be available from the RNIB in large print, Braille or audio CD. For further information please call the RNIB Medicine Leaflet line on 0800 198 5000. The product code(s) for this leaflet is/are: PL00010/0562.


Due to regulatory changes, the content of the following Patient Information Leaflet may vary from the one found in your medicine pack. Please compare the 'Leaflet prepared/revised date' towards the end of the leaflet to establish if there have been any changes.

If you have any doubts or queries about your medication, please contact your doctor or pharmacist.

Package Leaflet: Information for the user

Pro-Viron® 25mg tablet


Read all of this leaflet carefully before you start taking this medicine.

  • Keep this leaflet. You may need to read it again.
  • If you have any further questions, ask your doctor or pharmacist.
  • This medicine has been prescribed for you. Do not pass it on to others. It may harm them, even if their signs of illness are the same as yours.
  • If you get any side effects, talk to your doctor or pharmacist. This includes any possible side effects not listed in this leaflet. See section 4.

In this leaflet:

1. What Pro-Viron is and what it is used for
2. Before you take Pro-Viron
3. How to take Pro-Viron
4. Possible side effects
5. How to store Pro-Viron
6. Further information

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?

  • Pro-Viron is used in men who do not naturally produce enough androgens (male hormones).
  • 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:

  • you are allergic (hypersensitive) to mesterolone or any of the other ingredients of Pro-Viron (see Section 6: Further Information)
  • you have prostate cancer
  • you have (or have had) a liver tumour.

Take special care with Pro-Viron:

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

  • 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).
  • Pro-Viron contains methyl and propyl parabens which may cause allergic reactions (possibly delayed).

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.

  • The usual amount is one tablet, taken 3 or 4 times a day.
  • Swallow 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.

  • Discomfort 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).
  • Frequent 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: By reporting side effects you can help provide more information on the safety of this medicine.

5. How to store Pro-Viron

  • Keep this medicine out of the sight and reach of children.
  • Do 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.
  • Medicines 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

  • The active substance is mesterolone. Each tablet contains 25mg of mesterolone.
  • The 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


Bayer AG


Bayer Weimar GmbH &Co KG

This leaflet was last revised: August 2017


Company contact details

Company image

400 South Oak Way, Reading, Berkshire, RG2 6AD


+44 (0)118 206 3000

Before you contact this company: often several companies will market medicines with the same active ingredient. Please check that this is the correct company before contacting them. Why?

Active ingredients


Legal categories

POM - Prescription Only Medicine

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