Other names
Sildenafil
Impact of viagra on testosterone
Chronic treatment with sildenafil stimulates Leydig cell and testosterone secretion.
https://www.ncbi.nlm.nih.gov/pubmed/19659904
Mouse study: mice treated with Sildenafil showed a significant increase in testosterone serum levels
https://www.ncbi.nlm.nih.gov/pubmed/25239757?dopt=Abstract
Sildenafil = Testosterone and DHT up, LH down
https://www.ncbi.nlm.nih.gov/pubmed/24106072
Sildenafil treatment in vivo stimulates Leydig cell steroidogenesis via the cAMP/cGMP signaling pathway.
https://www.ncbi.nlm.nih.gov/pubmed/20663985
"In our studies, serum testosterone and ex vivo testosterone production significantly increased in sildenafil-treated animals."
Transient rise of serum testosterone level after single sildenafil treatment of adult male rats.
https://www.ncbi.nlm.nih.gov/pubmed/22429315
Serum FSH, SHBG and inhibin B levels remained unchanged.
http://onlinelibrary.wiley.com/doi/10.1111/j.2047-2927.2013.00131.x/full
Tolerance
It is possible that people may develop a tolerance to viagra over time.
Long term use study: tolerance not major issue
https://www.ncbi.nlm.nih.gov/pubmed/18516312/
3 years follow up - seems to keep working
https://www.ncbi.nlm.nih.gov/pubmed/12837433
Survey of users: possible evidence of tolerance
https://www.ncbi.nlm.nih.gov/pubmed/11490248
Design: Two surveys, one during the first year of sildenafil use, the next completed two years later.
Findings:
- Overall improvement rate in first survey was 74%.
- Second survey - only 52% had continued treatment.
-Of the 43 who were still using it 16 (37%) had to increase the dose by 50 mg. to achieve an adequate result.
- There was no significant relationship between the need to increase the dose and frequency of treatment per month. (This perhaps argues against the tolerance effect.)
- In those who had stopped using treatment, 14 (50%) patients discontinued sildenafil because of the loss of efficacy.
Letter to editor: Declining mental arousal could be the cause
http://www.jurology.com/article/S0022-5347(05)64885-9/abstract
(See letter from Rosemary Basson)
- Sildenafil's response is dependent on mental arousal.
- Returning mental arousal returns effect in patients in their clinic.
Letter to editor: Worsening cardiovascular condition could be the cause
Starts at the bottom of the page here: http://www.jurology.com/article/S0022-5347(05)64885-9/abstract
And ends at the start of the page here: http://www.jurology.com/article/S0022-5347(05)64887-2/abstract
- Many patients may have deteriorating cardiovascular condition/endothelial function
Letter to editor: University College London researchers have also noticed declining efficacy
http://www.jurology.com/article/S0022-5347(05)64889-6/abstract
Suggest 3 possible mechanisms
- Underlying factors are getting worse.
- Endothelin B receptors increase (responsible for penile contraction)
- Increased generation of superoxide anions (as exhibited in nitroglycerin tolerance).
[READ THIS LETTER AGAIN CAREFULLY]
Letter to editor: testosterone decline could be cause
http://www.jurology.com/article/S0022-5347(05)64887-2/abstract
See letter from Culley C Carson
Letter to editor: men were old, and health likely deteriorating - Also their data show that testosterone is highly related to sildenafil response
See letter from Andre T. Guay
Starts on this page: http://www.jurology.com/article/S0022-5347(05)64887-2/abstract
With supporting table on this page: http://www.jurology.com/article/S0022-5347(05)64890-2/abstract
In nitroglycerin tolerance the tolerance effect is attenuated by the provision of extra superoxide dismutase
https://www.ncbi.nlm.nih.gov/pubmed/7814613?access_num=7814613&link_type=MED&dopt=Abstract
Safety
Sildenafil may not permanently threaten vision
https://www.ncbi.nlm.nih.gov/pubmed/18818963/