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.
Safety at a Glance
High Risk- General Principles
- Start low, go slow: Always begin with a low dose, especially with unfamiliar batches or new substances. Individual se...
- Toxicity: Warning: Many psychoactive substances that are reasonably safe to use on their own can suddenly become dangerous and ...
- Dangerous with: Atropa belladonna, Datura, Diphenhydramine, Harmala alkaloid, 25x-NBOMe, 2C-T-x, DOx (+2 more)
- Overdose risk: Stimulant overdose from Fenethylline is a medical emergency primarily involving cardiovascular an...
If someone is in crisis, call 911 or Poison Control: 1-800-222-1222
Dosage
oral
Duration
oral
Total: 3 hrs – 4 hrsHow 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.
Subjective Effects
The effects listed below are based on the Subjective Effect Index (SEI), an open research literature based on anecdotal reports and personal analyses. They should be viewed with a healthy degree of skepticism. These effects will not necessarily occur in a predictable or reliable manner, although higher doses are more liable to induce the full spectrum of effects.
Physical Effects
Physical(14)
- Abnormal heartbeat— Abnormal heartbeat (arrhythmia) is any deviation from the heart's normal rhythm — including beats th...
- Appetite suppression— A distinct decrease in hunger and desire to eat, ranging from reduced interest in food to complete d...
- Bronchodilation— Bronchodilation is the widening of the bronchial airways in the lungs, reducing resistance to airflo...
- Dehydration— A state of insufficient bodily hydration manifesting as persistent thirst, dry mouth, and physical d...
- Dry mouth— A persistent, uncomfortable reduction in saliva production causing the mouth and throat to feel parc...
- Increased blood pressure— Increased blood pressure (hypertension) is an elevation of arterial pressure above the normal 120/80...
- Increased bodily temperature— Increased bodily temperature (hyperthermia) is an elevation of core body temperature above the norma...
- Increased heart rate— A noticeable acceleration of heartbeat that can range from a subtle awareness of one's pulse to a fo...
- Muscle cramp— Muscle cramps are sudden, involuntary, and often painful contractions of muscles that occur as a sid...
- Seizure— Uncontrolled brain electrical activity causing convulsions and loss of consciousness -- a life-threa...
- Stamina enhancement— Stamina enhancement is an increase in one's ability to sustain physical and mental exertion over ext...
- Stimulation— A state of heightened physical and mental energy characterized by increased wakefulness, elevated mo...
- Teeth grinding— An involuntary clenching and rhythmic grinding of the jaw muscles, known clinically as bruxism, that...
- Vasoconstriction— A narrowing of blood vessels throughout the body that produces sensations of cold extremities, tingl...
Cognitive & Perceptual Effects
Cognitive(11)
- Anxiety— Intense feelings of apprehension, worry, and dread that can range from a subtle background unease to...
- Cognitive euphoria— A cognitive and emotional state of intense well-being, elation, happiness, and joy that manifests as...
- Compulsive redosing— An overwhelming, difficult-to-resist urge to continuously take more of a substance in order to maint...
- Delusion— A delusion is a fixed, false belief that is held with unshakeable certainty and is impervious to con...
- Depression— A persistent state of low mood, emotional numbness, hopelessness, and diminished interest or pleasur...
- Irritability— Irritability is a sustained state of emotional reactivity in which the threshold for annoyance, frus...
- Motivation suppression— Motivation suppression is a state of diminished drive and willingness to engage in goal-directed beh...
- Panic attack— A panic attack is a discrete episode of acute, overwhelming fear or terror that arises suddenly and ...
- Paranoia— Irrational suspicion and belief that others are watching, plotting against, or intending harm toward...
- Thought loops— Becoming trapped in a repeating cycle of thoughts, actions, and emotions that loops every few second...
- Wakefulness— An increased ability to stay awake and alert without the desire to sleep. Distinct from stimulation ...
Pharmacology
- Conversion rate
24.5% of the weight of Fenethylline is metabolized to amphetamine and 13.7% to theophylline both of which are active stimulants.
Fenethylline became illegal in most countries in 1986 after being listed by the World Health Organization for international scheduling under the Convention on Psychotropic Substances.
Australia: Fenethylline is a Schedule 9 prohibited substance.
Brazil: Fenethylline is a Class A3 psychoactive substance.
Canada: Fenethylline is a Schedule III drug in Canada.
Germany: Fenethylline is a Anlage III(Schedule III) drug under the Betäubungsmittelgesetz(controlled substances law of Germany) and can only be obtained by prescription.
United Kingdom: Fenethylline is a Class C drug in the United Kingdom.
United States: Fenethylline is a Schedule I controlled substance in the United States.
Responsible use
Stimulant
Amphetamine
Fenethylline (Wikipedia)
Theophylline (Wikipedia)
Fenethylline (DrugBank)
Fenethylline (Isomer Design)
Fenethylline Abuse (Abuse Study)
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 |
| Alcohol | Uncertain | — |
| Caffeine | Uncertain | — |
| Cannabis | Uncertain | — |
| Cocaine | Uncertain | — |
| GBL | Uncertain | — |
History
Fenethylline was first synthesized by the German chemicals company Degussa AG in 1961
It was primarily marketed as a milder alternative to amphetamine, due to its lower potential for raising blood pressure, making it ideal for patients with cardiovascular disease. It was also used for the treatment of children with ADHD and less commonly narcolepsy.
Fenethylline's structure consists of an amphetamine molecule connected on the N position to a theophylline molecule at the R3 position by an ethyl group.
- Conversion rate
24.5% of the weight of Fenethylline is metabolized to amphetamine and 13.7% to theophylline both of which are active stimulants.
Fenethylline became illegal in most countries in 1986 after being listed by the World Health Organization for international scheduling under the Convention on Psychotropic Substances.
Australia: Fenethylline is a Schedule 9 prohibited substance.
Brazil: Fenethylline is a Class A3 psychoactive substance.
Canada: Fenethylline is a Schedule III drug in Canada.
Germany: Fenethylline is a Anlage III(Schedule III) drug under the Betäubungsmittelgesetz(controlled substances law of Germany) and can only be obtained by prescription.
United Kingdom: Fenethylline is a Class C drug in the United Kingdom.
United States: Fenethylline is a Schedule I controlled substance in the United States.
Responsible use
Stimulant
Amphetamine
Fenethylline (Wikipedia)
Theophylline (Wikipedia)
Fenethylline (DrugBank)
Fenethylline (Isomer Design)
Fenethylline Abuse (Abuse Study)
Harm Reduction
General Principles
- Start low, go slow: Always begin with a low dose, especially with unfamiliar batches or new substances. Individual sensitivity varies enormously.
- Test your substances: Use reagent test kits to verify identity and check for dangerous adulterants. Consider using drug checking services where available.
- Research thoroughly: Understand expected dose ranges, duration, potential interactions, and contraindications before use.
- Never use alone: Have a trusted, sober person present, especially with new substances or higher doses.
- Set and setting: Your mindset and environment profoundly influence the experience. Choose a safe, comfortable environment and ensure you're in a stable psychological state.
Fenethylline-Specific Harm Reduction
- Cardiovascular monitoring: Stimulants increase heart rate and blood pressure. Avoid strenuous physical activity and stay hydrated. Those with heart conditions should not use stimulants.
- Hydration and nutrition: Eat before and during use, even if appetite is suppressed. Set reminders to drink water regularly but avoid overhydration.
- Sleep: Do not redose to avoid the comedown. Set a firm cutoff time to allow adequate sleep. Sleep deprivation amplifies negative effects and health risks.
- Compulsive redosing: Many stimulants produce a strong urge to redose. Pre-measure your dose and commit to it. Remove access to additional substance if possible.
- Dental health: Bruxism (jaw clenching) can damage teeth. Use magnesium supplements and consider a mouth guard for longer sessions.
- Combination danger: Never combine with MAOIs — this can cause hypertensive crisis. Combining with other stimulants compounds cardiovascular risk.
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.
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 professionals
Prevention: 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.
Dangerous Interactions
The combinations listed below may be life-threatening. Independent research should always be conducted to ensure safety when combining substances.
Extreme cardiovascular strain from anticholinergic and stimulant effects combined
Extreme cardiovascular strain from anticholinergic and stimulant effects combined
Extreme cardiovascular strain from anticholinergic and stimulant effects combined
Risk of hypertensive crisis and serotonin syndrome; potentially fatal combination
Risk of hypertensive crisis and serotonin syndrome; potentially fatal combination
Tolerance
| Full | Develops with prolonged and repeated use |
| Half | 3 - 7 days |
| Zero | 1 - 2 weeks |
Cross-tolerances
Legal Status
Fenethylline became illegal in most countries in 1986 after being listed by the World Health Organization for international scheduling under the Convention on Psychotropic Substances.
Australia: Fenethylline is a Schedule 9 prohibited substance.
Brazil: Fenethylline is a Class A3 psychoactive substance.
Canada: Fenethylline is a Schedule III drug in Canada.
Germany: Fenethylline is a Anlage III(Schedule III) drug under the Betäubungsmittelgesetz(controlled substances law of Germany) and can only be obtained by prescription.
United Kingdom: Fenethylline is a Class C drug in the United Kingdom.
United States: Fenethylline is a Schedule I controlled substance in the United States.
Responsible use
Stimulant
Fenethylline (Wikipedia)
Theophylline (Wikipedia)
Fenethylline (DrugBank)
Fenethylline (Isomer Design)
Fenethylline Abuse (Abuse Study)
Tips (4)
Start low with Fenethylline and wait for full onset before redosing. Stimulant redosing extends duration and side effects more than it extends euphoria, while adding cardiovascular strain. Set a firm limit before you start.
Have a landing plan for the Fenethylline comedown. Prepare food, melatonin or magnesium, and a comfortable environment in advance. Avoid using depressants to manage the comedown as this creates polydrug dependency patterns.
Stay hydrated while using Fenethylline. Stimulants increase heart rate and body temperature while suppressing thirst signals. Sip water regularly, roughly 250-500ml per hour, more if dancing or in hot environments.
Monitor your heart rate and blood pressure when using Fenethylline. Sustained elevated cardiovascular stress causes cumulative damage. If you experience chest pain, irregular heartbeat, or numbness in extremities, seek medical attention.
See Also
References (4)
- Amphetamine: new content for an old topic — Heal et al. Neuropsychopharmacology Reviews (2013)paper
- PubChem: Fenethylline
PubChem compound page for Fenethylline (CID: 19527)
pubchem - Fenethylline - TripSit Factsheet
TripSit factsheet for Fenethylline
tripsit - Fenethylline - Wikipedia
Wikipedia article on Fenethylline
wikipedia