What kind of performance enhancers are PDE-5 inhibitors?

What kind of performance enhancers are PDE-5 inhibitors?

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Phosphodiesterase 5 (PDE-5) inhibitors were originally investigated for hypertension because of their ability to relax blood vessels. To researchers’ surprise, inhibiting PDE-5 was even better for improving male erection. That’s why PDE-5 inhibitors such as sildenafil or tadalafil are most commonly marketed for improving erectile function. Relaxing blood vessels may be beneficial for purposes of exercise. PDE-5 inhibitors have potential to increase endurance performance because it counteracts contraction of blood vessels in lungs [1].

Clinical studies have shown that sildenafil and tadalafil can improve exercise capacity in certain patient populations. A proof-of-concept study demonstrated somewhat increased aerobic exercise capacity in young adult patients with cystic fibrosis, a disease that reduces lung function [2]. 25 mg of sildenafil increased the VOmax approximately 5% after four weeks of use while a single 50 mg dose failed to increase VOmax significantly despite some tendency to do so. There is some data that tadalafil increases exercise capacity of patients with pulmonary hypertension . It must be noted that the study subjects were those who could not walk 4.5 km/h for 10 minutes [3] and about third of the patients suffered from headache as an side effect.

In diabetic but not in healthy women, tadalafil has been shown to increase glucose utilization in the muscle [5]. In cyclists, sildenafil did not improve the results in the context of 16.1 km exercise [1]. On the negatice side, tadalafil is associated with yet unexplained higher incidence of back pain in clinical studies. About 8.3% to 9.4% of men taking tadalafil suffered from back pain while only 3.4% of men in placebo group suffered from back pain — the risk is greater than two-fold [6]. There was no difference in blood parameters. Hence, the increased incidence of back pain lacks explanation. One might ask if the back pain is associated with increased strenuous sexual performance. Anabolic steroid users seem to use PDE-5 inhibitors mainly for sexual enhancement also [7]. In mice, PDE-5 inhibitors can increase the production of testosterone [8].

In men – possible but unlikely. The scientific consensus based on several human studies is that PDE-5 inhibitors do not increase testosterone production. PDE-5 inhibitors are beneficial for semen but, again, in infertile rather than healthy men [9]. It seems unlikely that PDE-5 inhibitors augment testosterone. It is the other way around, instead [10]. PDE-5 inhibitors are sexual performance enhancers that just happen to be performance enhancers in serious lung disease patients.

Don´t hesitate to ask it.

[1] https://pubmed.ncbi.nlm.nih.gov/30653578/
[2] https://pubmed.ncbi.nlm.nih.gov/31803404/
[3] https://pubmed.ncbi.nlm.nih.gov/19470885/
[4] https://pubmed.ncbi.nlm.nih.gov/4377045/
[5] https://pubmed.ncbi.nlm.nih.gov/20535445/
[6] https://pubmed.ncbi.nlm.nih.gov/16034469/
[7] https://pubmed.ncbi.nlm.nih.gov/31303195/
[8] https://pubmed.ncbi.nlm.nih.gov/19659904/
[9] https://pubmed.ncbi.nlm.nih.gov/28259808/
[10] https://pubmed.ncbi.nlm.nih.gov/24251448/

„Side effects” of some pharmaceuticals are researched as medicines against COVID-19


Chemicals that are designed for one particular purpose can have unexpected side effects – often adverse, sometimes useful. For example, according to anecdotal evidence one of the SARMs (that is not even scientifically tested in humans) can tint the vision green or yellow. However, it is not the side effects of SARMs this post will be about. This post is about current coronavirus COVID-19 or SARS-2 (Severe Acute Respiratory Syndrome 2), a very close relative of coronavirus that caused SARS, and somewhat less close relative to very lethal MERS (Middle East Respiratory Syndrome) and research pertaining to possible treatment.

As concerns the coronaviruses, chemical informatics has revealed that a molecule that has been designed as a SERM (selective estrogen receptor modulator) could be repurposed as a medicine against novel coronavirus [1]. Of course, a computer analysis is not comparable to the rigour of actual human study but the model seems to be legit. Some other molecules found by informatics approach include emodin that has been found as a drug candidate in an earlier study [2]. Emodin is not a SARM, though, it is principally a a molecule that is responsible for laxative and estrogenic properties of certain medicinal rhubarb species. Of note, also melatonin was a „hit” in the analyses that matched coronavirus against the drug database. No experimental data on melatonin and coronavirus was found from scientific literature, though. Nevertheless, in the melatonin is considered as a potential treatment in another white paper [3] and one of the potential mechanisms might be that melatonin does not allow the COVID-19 to kill off the hosts’ T-cells so easily [4]. It seems likely that elderberries may have the same mechanism combating the upper respiratory tract viruses [5]. The other effect of melatonin that may facilitate the favourable income include protection from reactive nitrogen species. Indeed, in addition to direct antiviral mechanisms, immune stimulation and immune stimulant drugs [6] are also considered, and the most promising one, interferon beta-1 peptide is indeed a working solution against coronavirus, and included into medical guidelines [7]. It is known that lack of interferon beta is responsible for lethal pneumonia [8], which is the key difference between serious and non-serious coronavirus infections.

MERS (Middle East Respiratory Syndrome) coronavirus was tested against several drugs. In that study, a drug against malaria, chloroquine, and a drug against parasites, nitazoxanide, also had a „side effect” against the virus that caused MERS, and these two were more than order of magnitude more selective and potent (in vitro, at least) against MERS than most of the antiviral drugs that are used in the hospitals against COVID coronavirus now [9]. Lately, chloroquine has been added to several treatment guidelines, and the United Kingdom banned the export of chloroquine [10]. A now rather uncommon drug that was formerly used to treat arthritis, indomethacin was very effective in treating both SARS and dogs’ coronavirus in dogs [11] and there is an impressive list of potential molecules that could help against coronavirus in the very earliest research phase [12].

Finally, a list of food supplements has been published that has been suggested to ameliorate respiratory tract infections caused by RNA viruses such as influenza and coronavirus in general [13]:

Substance Dose
Ferulic acid 500-1000 mg
Lipoic acid 1200-1800 mg (in place of ferulic acid)
Spirulina 15 g (or 100 mg PCB)
N-Acetylcysteine 1200–1,800 mg
Selenium 50-100 mcg
Glucosamine 3,000 mg or more
Zinc 30-50 mg
Yeast Beta-Glucan 250-500 mg
Elderberry 600–1500 mg

[1] https://www.ncbi.nlm.nih.gov/pubmed/32194980
[3] https://www.sciencedirect.com/science/article/pii/S0024320520303313
[4] https://onlinelibrary.wiley.com/doi/full/10.1046/j.1600-079X.2003.00105.x
[5] https://www.ncbi.nlm.nih.gov/pubmed/31560964
[6] https://www.ncbi.nlm.nih.gov/pubmed/32205350
[7] https://www.ncbi.nlm.nih.gov/pubmed/32164424
[8] https://www.ncbi.nlm.nih.gov/pubmed/26867177
[9] https://www.nature.com/articles/s41422-020-0282-0
[10] https://www.gov.uk/government/publications/medicines-that-cannot-be-parallel-exported-from-the-uk
[11] https://www.ncbi.nlm.nih.gov/pubmed/17302372
[12] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4195804/
[13] https://www.ncbi.nlm.nih.gov/pubmed/32061635