How long does Fenethylline last?

The total duration of Fenethylline via oral is 3 hours to 4 hours. Onset typically occurs within 1.5 hours to 2 hours.

Fenethylline — SubstanceWiki

Codrug of amphetamine and theophylline

Fenethylline (BAN, USAN) or fenetylline (INN) is a codrug of amphetamine and theophylline and so a mutual prodrug of both. It is also spelled phenethylline; other names for it are amphetaminoethyltheophylline and amfetyline. The drug was marketed for use as a psychostimulant under the brand names Captagon, Biocapton, and Fitton. The brand name "Captagon" (or in lowercase as "captagon") is often used generically to describe illicitly produced fenethylline.

Fenethylline is illegal in most countries. It is produced primarily for illicit use, which takes place mainly in Syria. The illicit global market for the drug was estimated in 2023 to be worth approximately US$57 billion.

Smuggling of fenethylline became Syria's principal export, exceeding the total of all other exports under the Assad regime during the Syrian civil war (20112024). It was the world's largest producer of the drug, accounting for about 80% of the global supply. A large quantity of Captagon tablets, ready for clandestine export, was captured by anti-Assad forces that took control of Damascus in December 2024.

How It Feels

Fenethylline, known colloquially as Captagon, presents a hybrid experience that reflects its dual pharmacological nature as a combination of amphetamine and theophylline. The onset is steady and measured, arriving over thirty to sixty minutes as a rising tide of alert, focused energy. There is none of the jarring rush of pure amphetamine. Instead, the stimulation builds smoothly, as though a dimmer switch for wakefulness and motivation were being slowly turned upward. The mind clears of fog and fatigue. Physical energy increases in tandem with mental sharpness.

At the peak, fenethylline produces a state of sustained, confident functionality. The experience is more rounded than pure amphetamine, with the theophylline component contributing a smooth, almost creamy quality to the stimulation that softens the harder edges. Concentration is excellent and can be maintained for extended periods without the jittery restlessness that often accompanies comparable doses of amphetamine alone. There is a mild but real euphoria, a sense of optimism and capability that makes demanding tasks feel achievable and even enjoyable. Social interaction is enhanced: conversations flow easily, confidence increases, and there is a charismatic energy that others may notice and respond to.

The physical effects are present but moderated by the combination. Heart rate increases, pupils dilate, and appetite is suppressed. The bronchodilatory effects of theophylline contribute to a sense of easy, deep breathing that can feel invigorating. Mild jaw tension and dry mouth are common. The overall physical load is lighter than an equivalent stimulation from pure amphetamine, though body temperature still rises and sweating may occur during physical activity. The combination produces a stimulation that is often described as cleaner and more sustainable than amphetamine alone, with less of the peripheral nervous system overdrive.

The effects last four to eight hours, tapering gradually into a mild fatigue and emotional flatness. The comedown is less punishing than pure amphetamine, though it follows the same general trajectory: a slow deflation of energy and confidence, replaced by tiredness and a desire for rest. Sleep may be delayed for several hours beyond the subjective end of the experience. The following day typically feels unremarkable, with perhaps a slight grogginess that resolves by midday. Fenethylline's reputation rests largely on this profile of sustained, functional stimulation with a relatively manageable side-effect burden.

Detection Methods

Standard Drug Panel Inclusion

Fenethylline (Captagon) is a prodrug that is metabolized into amphetamine and theophylline. Because it releases amphetamine upon metabolism, fenethylline will trigger a positive result on standard 5-panel immunoassay drug screens for amphetamines. The amphetamine metabolite is indistinguishable from amphetamine from any other source on standard immunoassays.

Urine Detection

After ingestion of fenethylline, amphetamine appears in urine within hours and is detectable for approximately 2 to 4 days. Theophylline, the other metabolic product, is detectable for approximately 1 to 2 days. The intact fenethylline parent compound is rapidly cleaved and is rarely detected in urine. The presence of both amphetamine and theophylline metabolites together can suggest fenethylline as the source, but this requires specific analytical methods.

Blood and Saliva Detection

Blood testing will detect amphetamine (from fenethylline metabolism) for approximately 24 to 48 hours. Intact fenethylline may be detectable briefly in blood shortly after ingestion, but the parent compound is rapidly hydrolyzed. Oral fluid testing will detect amphetamine for 24 to 50 hours.

Hair Follicle Detection

Hair testing will detect amphetamine from fenethylline use for up to 90 days. The presence of amphetamine in hair cannot distinguish between fenethylline, dextroamphetamine, or illicit amphetamine as the source without additional analysis for fenethylline-specific markers.

Confirmatory Testing

GC-MS and LC-MS/MS will confirm the presence of amphetamine in biological specimens from fenethylline use. Specialized analytical methods can detect intact fenethylline or specific metabolite ratios (amphetamine-to-theophylline) that may suggest fenethylline as the source, but this is primarily of forensic interest. Standard confirmatory testing does not differentiate fenethylline-derived amphetamine from other sources.

Reagent Testing

Fenethylline tablets (commonly branded as Captagon) react with Marquis reagent to produce an orange-brown color consistent with the amphetamine moiety. Mecke reagent shows minimal reaction. The distinctive biconvex tablet form with the Captagon logo is a visual identifier, but counterfeit Captagon tablets are extremely common and may contain amphetamine, methamphetamine, or other stimulants without fenethylline.

Interactions

Substance	Status	Note
Atropa belladonna	Dangerous	Extreme cardiovascular strain from anticholinergic and stimulant effects combined
Datura	Dangerous	Extreme cardiovascular strain from anticholinergic and stimulant effects combined
Diphenhydramine	Dangerous	Extreme cardiovascular strain from anticholinergic and stimulant effects combined
Harmala alkaloid	Dangerous	Risk of hypertensive crisis and serotonin syndrome; potentially fatal combination
Peganum harmala	Dangerous	Risk of hypertensive crisis and serotonin syndrome; potentially fatal combination
25x-NBOMe	Unsafe	—
2C-T-x	Unsafe	—
DOx	Unsafe	—
PCP	Unsafe	—
1,3-Butanediol	Caution	Increases anxiety, cardiovascular stress, and psychological intensity
25E-NBOH	Caution	Increases anxiety, cardiovascular stress, and psychological intensity
2C-T	Caution	Increases anxiety, cardiovascular stress, and psychological intensity
2C-T-2	Caution	Increases anxiety, cardiovascular stress, and psychological intensity
2C-T-21	Caution	Increases anxiety, cardiovascular stress, and psychological intensity
2C-T-7	Caution	Increases anxiety, cardiovascular stress, and psychological intensity
3-FMA	Caution	Increased cardiovascular strain and neurotoxicity risk
4-MMC	Caution	Increased cardiovascular strain and neurotoxicity risk
8-Chlorotheophylline	Caution	Increased cardiovascular strain and neurotoxicity risk
Adrafinil	Caution	Increased cardiovascular strain and neurotoxicity risk
Allylescaline	Caution	Increases anxiety, cardiovascular stress, and psychological intensity
Ayahuasca	Caution	Increases anxiety, cardiovascular stress, and psychological intensity
Benzydamine	Caution	Increased cardiovascular strain and neurotoxicity risk
Bromantane	Caution	Increased cardiovascular strain and neurotoxicity risk
Cake	Caution	Masks the effects of each drug; risk of overdosing when one wears off before the other
Deschloroetizolam	Caution	Masks the effects of each drug; risk of overdosing when one wears off before the other
Desomorphine	Caution	Stimulants mask opioid sedation, increasing overdose risk when the stimulant wears off
DET	Caution	Increases anxiety, cardiovascular stress, and psychological intensity
Dichloropane	Caution	Increased cardiovascular strain and neurotoxicity risk
Diclazepam	Caution	Masks the effects of each drug; risk of overdosing when one wears off before the other
DiPT	Caution	Increases anxiety, cardiovascular stress, and psychological intensity
DOM	Caution	Increases anxiety, cardiovascular stress, and psychological intensity
DPT	Caution	Increases anxiety, cardiovascular stress, and psychological intensity
Efavirenz	Caution	Increases anxiety, cardiovascular stress, and psychological intensity
Ephedrine	Caution	Increased cardiovascular strain and neurotoxicity risk
EPT	Caution	Increases anxiety, cardiovascular stress, and psychological intensity
Eszopiclone	Caution	Masks the effects of each drug; risk of overdosing when one wears off before the other
Etizolam	Caution	Masks the effects of each drug; risk of overdosing when one wears off before the other
Flubromazepam	Caution	Masks the effects of each drug; risk of overdosing when one wears off before the other
Flubromazolam	Caution	Masks the effects of each drug; risk of overdosing when one wears off before the other
Flunitrazepam	Caution	Masks the effects of each drug; risk of overdosing when one wears off before the other
Flunitrazolam	Caution	Masks the effects of each drug; risk of overdosing when one wears off before the other
Gaboxadol	Caution	Masks the effects of each drug; risk of overdosing when one wears off before the other
Hexedrone	Caution	Increased cardiovascular strain and neurotoxicity risk
Ibogaine	Caution	Increases anxiety, cardiovascular stress, and psychological intensity
Lorazepam	Caution	Masks the effects of each drug; risk of overdosing when one wears off before the other
Mephenaqualone	Caution	Masks the effects of each drug; risk of overdosing when one wears off before the other
MET	Caution	Increases anxiety, cardiovascular stress, and psychological intensity
Methallylescaline	Caution	Increases anxiety, cardiovascular stress, and psychological intensity
Methcathinone	Caution	Increased cardiovascular strain and neurotoxicity risk
Metizolam	Caution	Masks the effects of each drug; risk of overdosing when one wears off before the other
Midazolam	Caution	Masks the effects of each drug; risk of overdosing when one wears off before the other
MiPT	Caution	Increases anxiety, cardiovascular stress, and psychological intensity
MPT	Caution	Increases anxiety, cardiovascular stress, and psychological intensity
Naloxone	Caution	Stimulants mask opioid sedation, increasing overdose risk when the stimulant wears off
Nicotine	Caution	Increased cardiovascular strain and neurotoxicity risk
Nifoxipam	Caution	Masks the effects of each drug; risk of overdosing when one wears off before the other
Oxiracetam	Caution	Increased cardiovascular strain and neurotoxicity risk
Pentobarbital	Caution	Masks the effects of each drug; risk of overdosing when one wears off before the other
Phenobarbital	Caution	Masks the effects of each drug; risk of overdosing when one wears off before the other
Phenylpiracetam	Caution	Increased cardiovascular strain and neurotoxicity risk
Psilocybin Mushrooms	Caution	Increases anxiety, cardiovascular stress, and psychological intensity
Rhodiola Rosea	Caution	Increased cardiovascular strain and neurotoxicity risk
SAMe	Caution	Masks the effects of each drug; risk of overdosing when one wears off before the other
Alcohol	Uncertain	—
Caffeine	Uncertain	—
Cannabis	Uncertain	—
Cocaine	Uncertain	—
GHB	Uncertain	—
Ketamine	Uncertain	—

Showing 69 key interactions out of 72 total.

Toxicity & Safety

Warning: Many psychoactive substances that are reasonably safe to use on their own can suddenly become dangerous and even life-threatening when combined with certain other substances. The following list provides some known dangerous interactions (although it is not guaranteed to include all of them).

Always conduct independent research (e.g. Google, DuckDuckGo, PubMed) to ensure that a combination of two or more substances is safe to consume. Some of the listed interactions have been sourced from TripSit.

Alcohol - Drinking alcohol on stimulants is considered risky because it reduces the sedative effects of the alcohol that the body uses to gauge drunkenness. This often leads to excessive drinking with greatly reduced inhibitions, increasing the risk of liver damage and increased dehydration. The effects of stimulants will also allow one to drink past a point where they might normally pass out, increasing the risk. If you do decide to do this then you should set a limit of how much you will drink each hour and stick to it, bearing in mind that you will feel the alcohol and the stimulant less.
GHB/GBL - Stimulants increase respiration rate allowing a higher dose of sedatives. If the stimulant wears off first then the depressant effects of the GHB/GBL may overcome the user and cause respiratory arrest.
Opioids - Stimulants increase respiration rate allowing a higher dose of opiates. If the stimulant wears off first then the opiate may overcome the patient and cause respiratory arrest.
Cocaine - The rewarding effects of cocaine are mediated by DAT inhibition, and an increase of exocytosis of dopamine through the cell membrane. Amphetamine reverses the direction of DAT and the direction vesicular transports within the cell by a pH mediated mechanism of displacement, thus excludes the regular mechanism of dopamine release through means of exocytosis because the effects Na+/K+ ATPase are inhibited. You will find cardiac effects with the combination of cocaine and amphetamine due to a SERT mediated mechanism from the subsequent activation of 5-HT2B, which is an effect of serotonin-related valvulopathy. Amphetamines generally cause hypertension in models of abuse, and this combination can increase the chances of syncope due to turbulent blood flow during valve operation. The rewarding mechanisms of cocaine are reversed by administration of amphetamine.
Cannabis - Stimulants increase anxiety levels and the risk of thought loops and paranoia which can lead to negative experiences.
Caffeine - This combination of stimulants is generally considered unnecessary and may increase strain on the heart, as well as potentially causing anxiety and physical discomfort.
Tramadol - Tramadol and stimulants both increase the risk of seizures.
DXM - Both substances raise heart rate, in extreme cases, panic attacks caused by these substances have led to more serious heart issues.
Ketamine - Combining amphetamine and ketamine may result in psychoses that resemble schizophrenia, but not worse than the psychoses produced by either substance alone, but this is debatable. This is due to amphetamines ability to attenuated the disruption of working memory caused by ketamine. Amphetamine alone may result in grandiosity, paranoia, or somatic delusions with little to no effect on negative symptoms. Ketamine, however, will result in thought disorders, disruption of executive functioning, and delusions due to a modification of conception. These mechanisms are due to an increase of dopaminergic activity in the mesolimbic pathway caused by amphetamine due to its pharmacology effecting dopamine, and due to a disruption of dopaminergic functioning in the mesocortical pathways via NMDA antagonism effects of ketamine. Combining the two, you may expect mainly thought disorder along with positive symptoms.
PCP - Increases risk of tachycardia, hypertension, and manic states.
Methoxetamine - Increases risk of tachycardia, hypertension, and manic states.
Psychedelics (e.g. LSD, mescaline, psilocybin) - Increases risk of anxiety, paranoia, and thought loops.
25x-NBOMe - Amphetamines and NBOMes both provide considerable stimulation that when combined they can result in tachycardia, hypertension, vasoconstriction and, in extreme cases, heart failure. The anxiogenic and focusing effects of stimulants are also not good in combination with psychedelics as they can lead to unpleasant thought loops. NBOMes are known to cause seizures and stimulants can increase this risk.
2C-T-x - Suspected of mild MAOI properties. May increase the risk of hypertensive crisis.
5-MeO-xxT - Suspected of mild MAOI properties. May increase the risk of hypertensive crisis.
DOx
aMT - aMT has MAOI properties which may interact unfavorably with amphetamines.
MAOIs - MAO-B inhibitors can increase the potency and duration of phenethylamines unpredictably. MAO-A inhibitors with amphetamine can lead to hypertensive crises.

Overdose Information

Stimulant overdose from Fenethylline is a medical emergency primarily involving cardiovascular and neurological toxicity.

Signs of overdose: Extremely rapid or irregular heartbeat, chest pain, severe headache, dangerously elevated body temperature, seizures, agitation progressing to psychosis, confusion, and loss of consciousness.Emergency response:

Call emergency services immediately
Keep the person cool (remove excess clothing, apply cool water)
If seizures occur, protect the head and clear the area of hard objects
If the person loses consciousness, place in recovery position
Do not give the person more stimulants, caffeine, or depressants unless directed by medical professionalsPrevention: Pre-measure doses. Avoid redosing. Stay hydrated (but don't overhydrate). Take breaks from physical activity. Monitor heart rate if possible. Have someone present who can recognize warning signs.

Full	Unknown
Half	Unknown
Zero	Unknown

Fenethylline

Quick Dosage

Dosage

oral

Duration

oral

How It Feels

Subjective Effects

Physical Effects

Physical(7)

Cognitive & Perceptual Effects

Cognitive(7)

Pharmacology

Detection Methods

Standard Drug Panel Inclusion

Urine Detection

Blood and Saliva Detection

Hair Follicle Detection

Confirmatory Testing

Reagent Testing

Interactions

History

Harm Reduction

General Principles

Fenethylline-Specific Harm Reduction

Toxicity & Safety

Overdose Information

Dangerous Interactions

Tolerance

Legal Status

Experience Reports (2)

Tips (4)

See Also

References (5)

Frequently Asked Questions