Discovered by Pfizer and approved for use in Viagra on March 27, 1998, sildenafil is a PDE5 inhibitor. Sildenafil inhibits PDE5, leading to increased blood flow in the corpus cavernosum of the penis, and thus to firmer erections. Analogues of sildenafil, such as acetildenafil, are created to avoid detection by the usual methods of testing for sildenafil, and to bypass regulatory laws. Analogues typically have similar effects to the original compound. The number of analogues of sildenafil is increasing, and their types are unknown. Such analogues have been discovered in dietary and herbal supplements and sexual stimulants.
Sildenafil is significantly more potent than other phosphodiesterases, and this high potency raises concerns about potential side effects. For example, sildenafil might inhibit PDE3, which is involved in the control of cardiac contractility. Sildenafil also inhibits PDE6, an enzyme in the retina, leading to abnormalities related to color vision. Analogues of sildenafil can induce similar side effects, but because they are unregulated, it is impossible to determine their potency, and scientists are not sure in each case how to detect the analogues.
The most important concern about sildenafil is its structural analogues. Structural analogues are chemical compounds with slightly altered chemical structures. Structural analogues of sildenafil have similar effects on the body but are not subject to the same FDA requirements, and thus might have unknown and harmful side-effects. Recent research has shown that the volume and variety of sildenafil analogues have been increasing. In one study published in the Journal of Food and Drug Analysis, about half of the products analyzed were found to contain undeclared synthetic PDE5 inhibitors. Many jurisdictions have laws banning analogues of illegal drugs of abuse, but few have laws banning analogues of prescription drugs.
Known Side Effects of Sildenafil
The most commonly reported side effects of sildenafil are headaches, flushing of the face, upset stomach and nasal congestion. Other, less common, side effects include sensitivity to light, blurred vision, urinary tract infection, diarrhea and dizziness. Sildenafil might also share common side effects of some prescription medications, including antihistamines, antidepressants, antihypertensives, antipsychotics, beta blockers, diuretics, tranquilizers, appetite suppressants, cimetidine (Tagamet) and finasteride (Propecia).
Because analogues of sildenafil are found most often in herbal and dietary supplements and herbal sexual stimulants. Be sure to get as much detailed information regarding ingredients before using these products.