Glossary
The medical and regulatory terms used across this site, in plain language. Each definition is written from the source named under it, and links to the guide that explains it in full.
A
- Absolute risk
- The chance that a certain event will happen, for example to a person over a set period of time. It shows how likely something is, where relative risk only shows how two groups compare.
- Active ingredient
- The part of a medicine that provides its drug effect. A generic must contain the same active ingredient, in the same amount, as the brand.
- Alpha-blocker
- A medicine that relaxes muscle in blood vessels and the prostate, used for enlarged prostate (BPH) and high blood pressure. Because PDE5 inhibitors also lower blood pressure, the labels advise caution when the two are used together.
- Alprostadil
- A medicine that widens blood vessels and is used to treat ED. CAVERJECT, an injectable form, is approved to treat ED and to help clinicians test for it.
- ANDA (Abbreviated New Drug Application)
- The application a company files with FDA to approve a generic drug. It is called abbreviated because it generally does not repeat the animal and human studies; instead the company must show its product is bioequivalent to the brand.
- Atherosclerosis
- A condition in which plaque, a sticky mix of cholesterol, fat, calcium and other substances, builds up inside the arteries. Over time the plaque hardens and narrows them, which limits blood flow. NIDDK lists it among the blood vessel diseases that can lead to ED.
- Avanafil
- A PDE5 inhibitor approved to treat ED in adult men. It works the same way as the others in its class, by strengthening the nitric oxide signal during sexual stimulation.
B
- Bioequivalence
- The requirement that a generic drug deliver the same amount of active ingredient at the same rate and to the same extent as the brand name drug. FDA calls it a key requirement before it approves a generic.
- BPH (benign prostatic hyperplasia)
- A noncancerous enlargement of the prostate that can press on the urethra and slow or block urine flow. NIDDK lists an enlarged prostate among the conditions that can lead to ED, and tadalafil is approved to treat its urinary symptoms.
- Brand name drug
- A drug sold under a proprietary, trademark-protected name, such as Viagra or Cialis.
- Bremelanotide
- An injectable medicine approved for premenopausal women with a specific low-desire condition (hypoactive sexual desire disorder). MedlinePlus states it should not be used in men or to improve sexual performance.
C
- cGMP
- A messenger chemical whose levels rise when nitric oxide is released during arousal. More cGMP relaxes the smooth muscle in the penis so blood can flow in. The enzyme PDE5 breaks cGMP down, and PDE5 inhibitors slow that breakdown.
- Clinical trial
- A research study that tests how well a medical approach, such as a new treatment or test, works in people.
- Cohort study
- A study that follows groups of people who are alike in many ways but differ in one characteristic, such as smoking, and compares an outcome between them.
- Collagenase (Xiaflex)
- An enzyme that breaks down collagen, injected directly into the plaque of Peyronie's disease. NIDDK describes intralesional collagenase as the only FDA-approved treatment for Peyronie's disease, approved for curves of more than 30 degrees. It is not a treatment for ED.
- Compounded drug
- A medicine mixed or altered by a pharmacist or physician for a patient whose needs an approved drug cannot meet, for example someone allergic to a dye. FDA states that compounded drugs are not FDA-approved: FDA does not check their safety, effectiveness or quality before they are sold.
- Constriction ring
- The elastic ring that comes with a vacuum erection device. It helps keep the erection after the vacuum has drawn blood into the penis.
- Corpus cavernosum
- The tissue inside the penis where nitric oxide is released during sexual stimulation. When its smooth muscle relaxes, blood flows in and an erection follows.
- Counterfeit medicine
- A fake medicine passed off as the real thing. FDA warns it may contain the wrong ingredient, too much, too little or none of the active ingredient, or other harmful ingredients, and advises buying only from state-licensed pharmacies.
- CYP3A4
- An enzyme that helps break down many medicines, including in the small intestine. When something blocks it, more of a drug can enter the blood and stay longer. The sildenafil label notes that strong CYP3A4 inhibitors raise sildenafil levels.
D
- DailyMed
- A National Library of Medicine database of drug labeling submitted to FDA, including the prescribing information and patient labeling for prescription drugs. It is where this site reads the current ED medicine labels.
- De Novo classification
- An FDA pathway for a new type of device that has no legally marketed device to compare against. It classifies the device as Class I or II based on risk, and the device can then be marketed and used as a comparison for later devices.
- Device classification (Class I, II, III)
- FDA sorts medical devices into three classes by risk, Class I lowest and Class III highest. The class decides what review a device needs before sale: a Class I or II device that is not exempt needs a 510(k) submission. Device status on this site is taken only from FDA's own device records.
- Dietary supplement
- A product taken by mouth that contains a dietary ingredient, such as a vitamin, mineral, herb or amino acid, meant to supplement the diet. FDA does not approve supplements before they are sold, and a supplement label that makes certain claims must say the product is not intended to diagnose, treat, cure or prevent any disease.
E
- Endothelial cells
- The main type of cell lining the inside of blood vessels, lymph vessels and the heart.
- Erectile dysfunction (ED)
- A condition that keeps you from getting or keeping an erection firm enough for sex. Impotence is an older name for it that is used less now. It is common, and it often can be treated.
F
- FDA-approved
- For a drug, it means the company submitted clinical data and other information and FDA found that the drug's benefits outweigh its risks for a specific use, with approved labeling on how to use it safely. Safe here does not mean free of side effects.
G
- Generic drug
- A drug that is the same as a brand name drug in dosage form, safety, strength, how it is taken, quality, performance and intended use. By law it must contain the same amount of the same active ingredient. FDA allows minor differences in appearance, such as color, that do not change how the medicine works.
- Grafting
- A Peyronie's surgery that removes the plaque and replaces it with a patch of tissue taken from elsewhere in the body, grown in a laboratory or from a donor. Some men have numbness of the penis or ED afterward.
- Grapefruit interaction
- Grapefruit and its juice can block the CYP3A4 enzyme in the intestine, so more of some drugs enters the blood. FDA notes the effect differs by person, by drug and by how much juice is drunk, and that a pharmacist can say whether a given medicine is affected.
H
- Hypogonadism
- A condition in which the sex glands make little or no hormone; in men, the testes. It can start in the testes themselves or in the brain centers that control them.
I
- IIEF-5
- A shortened, five-question version of the IIEF, developed to help identify whether ED is present and how severe it is. Its items focus on erectile function and intercourse satisfaction.
- IIEF (International Index of Erectile Function)
- A 15-question, self-completed questionnaire built to measure erectile function and to detect changes with treatment. It covers five areas: erectile function, orgasmic function, sexual desire, intercourse satisfaction and overall satisfaction. ED trials often report results as IIEF scores.
- In-office injection test
- A test in which a clinician injects a medicine into the penis to see whether it can become erect, how full it gets and how long the erection lasts. It is usually done in the clinician's office.
- Intracavernosal injection
- An ED treatment in which a medicine is injected into the penis, causing an erection by increasing blood flow. A clinician teaches the patient how to give the injection.
- Intralesional injection
- An injection of medicine directly into a plaque, used in Peyronie's disease. It is done in a clinician's office, and the area is often numbed first.
- Investigational
- Describes a drug or procedure that FDA has allowed to be tested in people but has not approved for the use being studied. A drug can be approved for one condition and still be investigational for another.
L
- Libido
- Sexual desire, or the mental energy and emotion related to sex. Desire is separate from erection: ED medicines help erections but do not raise desire.
- Low-intensity shockwave therapy (LiSWT)
- A treatment that uses sound waves with the aim of improving blood flow to the penis. A 2025 Cochrane review found it may have a small short-term effect that men may not find clinically important, and rated the certainty of all its evidence as low.
- Luteinizing hormone (LH)
- A hormone made in the pituitary gland. In men it signals the testes to make testosterone.
M
- Medication Guide and Patient Package Insert
- Plain-language information written for patients on how to use a drug safely. It is part of a drug's labeling, alongside the prescribing information.
- MedWatch
- FDA's Safety Information and Adverse Event Reporting Program. Patients and clinicians can use it to report side effects or problems with a medicine or a product, and reports can lead FDA to update labels or issue safety alerts.
- Meta-analysis
- A method that combines data from several studies of the same question. NCI notes its results are usually stronger than any one study by itself.
N
- NAION
- A rare condition in which reduced blood flow damages the optic nerve and causes sudden vision loss, which can be permanent. It has been reported rarely in men taking any PDE5 inhibitor. The labels say to stop the medicine and get medical care right away for sudden vision loss in one or both eyes.
- NDA (New Drug Application)
- The application a drug's sponsor submits when it believes it has enough evidence of safety and effectiveness for FDA approval. If FDA approves it, the product may be marketed in the United States.
- Nerve-sparing surgery
- Surgery that tries to save the nerves near the tissue being removed. In prostate surgery, these include the nerves involved in erections.
- NIDDK
- Part of the US National Institutes of Health. It publishes plain-language health information on urologic conditions, including ED and Peyronie's disease, which this site cites throughout.
- Nitrates
- Medicines such as nitroglycerin that widen blood vessels and are used for chest pain (angina). The ED medicine labels say a PDE5 inhibitor must not be taken with nitrates or nitrites in any form, because together they can drop blood pressure too far.
- Nitric oxide (NO)
- A signaling molecule released in the penis during sexual stimulation. It starts the chain of steps that relaxes smooth muscle and lets blood flow in. PDE5 inhibitors work by strengthening the effect of nitric oxide, which is why they need arousal to work.
- Nitrite poppers
- Products containing chemicals similar to amyl nitrite that are inhaled or swallowed recreationally. FDA says they have not been evaluated for safe use and can cause extreme drops in blood pressure, breathing problems, seizures and death. Nitrites are also on the ED medicine labels' list of things never to combine with a PDE5 inhibitor.
- Nocturnal erection test
- A test that checks for the erections that happen during sleep. It can help a clinician tell whether ED has a physical cause. It may be done at home or in a sleep lab.
O
- Observational study
- A study in which researchers observe people or measure outcomes without trying to change them, for example without giving a treatment.
- Off-label use
- Using an FDA-approved drug for a use, condition or group of patients that is not in its approved labeling. It is legal when a clinician prescribes it, but FDA has not reviewed the benefits and risks for that use.
- Orange Book
- FDA's publication of drug products approved on the basis of safety and effectiveness, with their therapeutic equivalence ratings and patent information. You can search it to see whether a generic version of a drug is approved.
- Orthostatic hypotension
- A drop in blood pressure when you move from lying down to standing, which can cause dizziness or lightheadedness. It usually lasts seconds to minutes.
- Over-the-counter (OTC) drug
- A drug FDA has found safe and effective for use by the general public without a doctor's prescription.
P
- PDE5 inhibitor
- The class of oral medicines most often prescribed for ED, which includes sildenafil, tadalafil, vardenafil and avanafil. They block an enzyme called PDE5, which strengthens the body's own erection signal and improves blood flow to the penis. They work with sexual stimulation, not in place of it.
- Penile arterial reconstruction
- Surgery to repair arteries so more blood can flow to the penis. NIDDK notes that it works best for younger men.
- Penile prosthesis
- A device placed in the penis during surgery that makes an erection possible. Types include an inflatable device worked by a pump in the scrotum and a firm rod. Most men with ED do not need surgery; an implant is usually considered after other treatments have not worked.
- Penile ultrasound
- An imaging test that shows how blood flows through the penis. It is one of the tests a clinician may use to look for the cause of ED.
- Peyronie's disease
- A disorder in which scar tissue, called plaque, forms under the skin of the penis and pulls on the surrounding tissue, so the penis curves or bends, usually during an erection. The plaque is benign: it is not cancer and not a tumor. ED can develop or get worse in its later phase.
- Pharmacokinetics
- What happens to a drug in the body over time: how it is absorbed, spread through the body and removed. Drug labels have a pharmacokinetics section that describes these steps.
- Placebo
- An inactive substance or treatment that looks the same as, and is given the same way as, the drug being tested. Trials compare the drug's effects with the placebo's.
- Plaque (Peyronie's disease)
- The scar tissue that forms in the tunica albuginea in Peyronie's disease. It is not the same as the plaque that builds up in arteries, and it is not cancerous.
- Plication
- A Peyronie's surgery that removes or pinches a piece of the tunica albuginea on the side opposite the plaque to straighten the penis. NIDDK notes it is less likely to cause numbness or ED than grafting, but it cannot restore length and the penis may become shorter.
- Prescribing information (drug label)
- The FDA-approved official description of a prescription drug: what it is used for, who should take it, its side effects, warnings and interactions, and safety information. The articles on this site cite these labels for drug facts.
- Prescription drug
- A drug that requires a clinician's authorization to buy.
- Priapism
- An erection that will not go away. The ED medicine labels and NIDDK say an erection lasting longer than 4 hours needs medical care right away, because untreated priapism can damage penile tissue and cause permanent loss of erections.
- Prolactin
- A hormone made by the pituitary gland. Higher-than-normal levels, called hyperprolactinemia, can affect how the testicles work in men and can cause lower sex drive and ED.
R
- Radical prostatectomy
- Surgery to remove the whole prostate and some tissue around it. Surgeons try to protect the nerves that control erection and the bladder.
- Randomized controlled trial
- A study in which participants are divided by chance into groups that get different treatments. Using chance makes the groups similar, so their results can be compared more fairly.
- Relative risk
- How the risk of an event in one group compares with the risk in another. A relative risk of one means no difference between the groups; above one means higher risk, below one means lower.
- Retrograde ejaculation
- When semen goes backward into the bladder instead of out through the urethra. It is uncommon and most often happens when the bladder opening does not close; some medicines can cause it.
S
- Sildenafil
- A PDE5 inhibitor that treats ED by increasing blood flow to the penis during sexual stimulation. It does not cure ED or raise sexual desire. The same ingredient is sold under another brand for pulmonary arterial hypertension, a different condition.
- Sudden sensorineural hearing loss
- An unexplained, rapid loss of hearing, all at once or over a few days, often in one ear. NIDCD calls it a medical emergency. The ED medicine labels tell patients to stop the medicine and get prompt care for a sudden decrease or loss of hearing.
T
- Tadalafil
- A PDE5 inhibitor approved for ED, for the urinary symptoms of an enlarged prostate (BPH), and for both together. Like the others in its class, it does not cure ED or raise sexual desire.
- Tainted product (hidden ingredient)
- A product whose label leaves out ingredients it contains, often prescription drug ingredients, banned substances or harmful chemicals. FDA calls these a type of medication health fraud. FDA's notifications for sexual enhancement products most often name sildenafil or tadalafil as the hidden drug.
- Therapeutic equivalence
- FDA's finding that one approved drug can be substituted for another with the full expectation of the same clinical effect and safety. FDA records these ratings in the Orange Book.
- Thyroid hormone
- A hormone from the thyroid gland that affects heart rate, blood pressure, body temperature and weight. Too little of it is called hypothyroidism. NIDDK lists thyroid imbalance among the hormone problems that can lead to ED.
- Total testosterone
- A blood test that measures both the testosterone bound to proteins and the unbound (free) testosterone. It is the most common testosterone test; free testosterone can also be measured on its own.
- Tunica albuginea
- The thick, elastic membrane inside the penis that helps keep it stiff during an erection. In Peyronie's disease, scar tissue (plaque) builds up in this layer.
U
- Urethral suppository
- A small solid piece of medicine placed into the urethra, the tube urine passes through, to help produce an erection. Some men with ED prefer it to an injection.
- Urologist
- A doctor with special training in diagnosing and treating diseases of the urinary organs, and of the reproductive organs in men. Urologists are among the clinicians who diagnose and treat ED.
V
- Vacuum erection device (VED)
- A device that pulls blood into the penis to create an erection. It has three parts: a plastic tube placed around the penis, a pump that creates a vacuum, and an elastic ring that helps keep the erection. It can take practice, and it can leave the penis feeling cold or numb or looking bruised.
- Vardenafil
- A PDE5 inhibitor that treats ED by increasing blood flow to the penis during sexual stimulation. It comes as a regular tablet and as a tablet that dissolves in the mouth. It does not cure ED or raise sexual desire.