PDE5 inhibitors: what they do and how to stay safe
PDE5 inhibitors are a group of medicines most people know for treating erectile dysfunction (ED). The common names are sildenafil (Viagra), tadalafil (Cialis), vardenafil (Levitra) and avanafil (Stendra). Doctors also use some of these drugs for pulmonary arterial hypertension under different doses and brand names. If you’re thinking about using one, you should know what they do, how they differ, and which safety rules matter most.
How they work is straightforward: they block an enzyme called phosphodiesterase type 5 (PDE5). That boosts a molecule called cGMP in the blood vessels of the penis, helping them relax and let blood flow in during sexual arousal. The effect depends on sexual stimulation — these drugs don’t cause erections on their own. For pulmonary hypertension, the same pathway lowers pressure in the lungs, which helps breathing and exercise tolerance.
Common drugs and usual uses
Sildenafil and vardenafil act faster but last shorter. Tadalafil can last up to 36 hours in the body and also has a daily low-dose option. Avanafil tends to act very quickly in some people. For ED, pills are usually taken before sex; tadalafil has a daily option if you prefer spontaneous activity. For lung conditions, dosing is different and guided by a specialist.
Safety, side effects, and interactions
Never take a PDE5 inhibitor with nitrates (nitroglycerin, isosorbide) — that combo can cause a dangerous drop in blood pressure. Be careful with alpha-blockers, some blood pressure meds, and strong CYP3A4 inhibitors (like certain antifungals and HIV meds) — they can raise PDE5 drug levels. Grapefruit and grapefruit juice may increase levels too, so ask your provider. Common side effects are headache, flushing, nasal congestion, upset stomach, or mild vision changes. Rare but serious issues include sudden vision or hearing loss and priapism (an erection lasting more than 4 hours) — seek emergency care if these happen.
People with unstable heart disease, recent stroke, low blood pressure, or severe liver or kidney problems need a doctor’s clearance before using these medicines. Older adults may need lower starting doses. If you’re on multiple heart meds, bring a complete list to your prescriber so they can choose the safest option.
Buying these meds online? Only use licensed pharmacies that require a prescription. Red flags include no prescription requirement, very low prices that look too good to be true, unclear contact details, or poor site security. Look for clear shipping info, a pharmacist contact, and verified customer reviews. If you order, check the packaging and batch numbers; counterfeit pills can look real but be ineffective or unsafe.
Practical tips: start with the lowest recommended dose, avoid heavy drinking before taking the pill, and don’t mix with recreational nitrates (poppers). Try the pill on a day when you can test timing and side effects in a safe setting. Talk to your doctor about daily vs as-needed dosing, and always report serious side effects right away. With a little care, PDE5 inhibitors can work well and safely for many people.
