At a glance
- For FDA-approved sildenafil, the timing is documented: peak levels 30–120 minutes after a dose, a half-life of about 4 hours, and an effect on erections shown up to about 4 hours, weaker at 4 hours than at 2.
- Common side effects – headache, flushing, indigestion, vision tint – rise with dose.
- For Kamagra, none of this has been verified: its content is unchecked, so how long it lasts and what side effects it causes cannot be predicted.
- Approved sildenafil did not affect sperm motility or shape after a single 100 mg dose; no such data exist for Kamagra.
How sildenafil works
Sildenafil blocks PDE5, an enzyme that limits blood flow to the penis; with sexual stimulation, this allows an erection. Without stimulation, it has no effect.[1]
How long approved sildenafil lasts
| Measure | Value |
|---|---|
| Taken | About 1 hour before sex; 30 minutes to 4 hours before |
| Peak blood level | 30–120 minutes (median 60) on an empty stomach |
| High-fat meal | Delays peak by about 60 minutes |
| Half-life | About 4 hours |
| Effect on erections | Shown up to about 4 hours, weaker at 4 than at 2 hours |
| Blood-pressure effect | Largest 1–2 hours after dose, gone by 8 hours |
All values from the Viagra prescribing information.[1] For comparison, tadalafil (Cialis) lasts much longer – see Viagra vs. Cialis.
Side effects of approved sildenafil
| Side effect | 25 mg | 50 mg | 100 mg | Placebo |
|---|---|---|---|---|
| Headache | 16% | 21% | 28% | 7% |
| Flushing | 10% | 19% | 18% | 2% |
| Indigestion | 3% | 9% | 17% | 2% |
| Abnormal vision | 1% | 2% | 11% | 1% |
| Effect | Level | Action |
|---|---|---|
| Erection longer than 4 hours | ■ Emergency | Emergency care |
| Sudden vision or hearing loss | ■ Emergency | Stop and get care at once |
| Chest pain during sex | ■ Emergency | Stop and get help |
| Taken with nitrates or riociguat | ■ Emergency | Never – dangerous drop in blood pressure |
Full guide: sildenafil side effects.
Sperm and fertility
In healthy volunteers, a single 100 mg oral dose of sildenafil had no effect on sperm motility or morphology. These data come from approved sildenafil of known strength; no comparable data exist for Kamagra.[1][2]
What stays unknown for Kamagra
| Question | FDA-approved sildenafil | Kamagra |
|---|---|---|
| Amount of active ingredient per tablet | Checked | Seller’s claim only |
| Onset and duration | In the FDA label | No reviewed data |
| Side-effect profile | From trials and monitoring | Depends on actual content |
| Effect on sperm | No effect in a single-dose study | Not studied |
| Record in FDA databases | Yes | None |
FDA warns that medicines from unlicensed sellers can contain too much or too little active ingredient, the wrong ingredient or none at all – which changes both how long a product works and what it does.[3]
Questions people ask
How long does Kamagra last?
How long does Viagra take to work?
Does Kamagra have the same side effects as Viagra?
Does sildenafil affect sperm?
Can I take a second dose if it wears off?
What is the legal alternative?
Conclusion: what we know, what we don’t, and what follows
What we know today
Established
- For FDA-approved sildenafil, timing (peak at 30–120 minutes, half-life about 4 hours) and side effects are documented in its label.[1]
- A single 100 mg dose did not affect sperm motility or shape in healthy volunteers.[1]
- Kamagra has no FDA application, labeling or NDC listing.[2]
What we don’t know yet
- How long Kamagra lasts, which side effects it causes and how it affects fertility cannot be known without verified content and studies, which do not exist.[2][3]
Bottom line
Questions about how long Kamagra lasts or how it compares with Viagra assume that both contain the same thing. For approved sildenafil, the answers are precise and published; for Kamagra, they are guesses built on the label of a different product. That gap – not price or brand – is the real difference between them, and it is why the approved medicine is the only one whose effects can actually be predicted.
Sources
- FDA: VIAGRA (sildenafil citrate) prescribing information, 2017 (PDF)
- openFDA and FDA National Drug Code Directory – no record for Kamagra (iMedix query, accessed September 28, 2026)
- FDA: BeSafeRx
- FDA: Generic Drug Facts (PDF)
Sources checked October 11, 2026.
