Terbutaline is a selective beta-2 adrenergic agonist: a drug that opens the airways by relaxing the smooth muscle around them. In the US it is sold as oral tablets (Brethine and generics) and as an injection given under the skin, both approved to prevent and reverse bronchospasm (narrowing of the airways) in asthma, bronchitis and emphysema. It is not a steroid or a hormone.
The most important safety fact is a boxed warning that FDA added in 2011. Terbutaline must not be used for prolonged treatment of preterm labor, because of maternal heart problems and deaths. Outside medicine, terbutaline draws interest as a relative of clenbuterol and albuterol. A handful of small Danish trials in healthy young men found modest lean-mass and sprint-power gains, some at doses above normal medical use. It is prohibited in sport at all times.
This page summarizes what the FDA labels, the FDA safety record, clinical trials and the World Anti-Doping Agency (WADA) report. It is for education only and is not medical advice.
| Property | Detail |
|---|---|
| Drug class | Selective beta-2 adrenergic agonist (sympathomimetic bronchodilator); not a steroid |
| Brands / US approval | Brethine tablets (NDA 017849, approved 1976); generic tablets and injection |
| US routes | Oral tablet; subcutaneous injection. US inhaler products (Brethaire, Bricanyl aerosol) are discontinued |
| Strengths | Tablets 2.5 mg and 5 mg; injection 1 mg/mL |
| Labeled adult dose | Oral 5 mg three times daily, max 15 mg/24 h; injection 0.25 mg, max 0.5 mg in 4 h |
| Half-life (labels) | About 3.4 h after oral dosing in asthma patients; 5.7 h mean terminal half-life after a 0.5 mg injection |
| Boxed warning | Not for prolonged tocolysis (stopping preterm labor); oral form not for any tocolysis |
| US status | Prescription only |
| WADA status | Prohibited at all times (S3 beta-2 agonists); no inhaled-dose exception for terbutaline |
What it is
Terbutaline is a small synthetic catecholamine-like molecule, 5-[2-(tert-butylamino)-1-hydroxyethyl]benzene-1,3-diol, with the formula C₁₂H₁₉NO₃ and a molecular weight of 225.28 g/mol (PubChem). The medicine is the sulfate salt, (C₁₂H₁₉NO₃)₂·H₂SO₄, molecular weight 548.65. A 5 mg tablet of terbutaline sulfate contains 4.1 mg of the free base (tablet label).
Bricanyl injection and tablets were approved in the US in 1974 and 1975 (Drugs@FDA, NDA 017466; Drugs@FDA, NDA 017618); both brand products are now discontinued. Brethine tablets remain listed as a prescription product (Drugs@FDA, NDA 017849). The metered-dose inhalers once sold in the US are discontinued (Drugs@FDA, NDA 018762; NDA 018000).
How it works
According to the labels, terbutaline acts preferentially on beta-2 receptors (tablet label):
- Stimulating the receptor activates adenylyl cyclase, which raises cyclic AMP (cAMP) inside the cell.
- Higher cAMP relaxes bronchial smooth muscle and reduces the release of allergy mediators from mast cells.
- Beta-2 receptors also exist in the human heart, at a concentration of 10–50% per the label; their precise function has not been established.
The tablet label notes that pulmonary function changed proportionally more than heart rate or blood pressure after oral dosing. The injection label states that controlled studies of subcutaneous terbutaline did not show a preferential beta-2 effect (injection label).
Pharmacokinetics
From the US tablet and injection labels:
| Parameter | Oral 5 mg tablet | Subcutaneous 0.5 mg |
|---|---|---|
| Subjects | 17 healthy men | 17 healthy men |
| Mean peak plasma level | 8.3 ng/mL | 9.6 ng/mL |
| Median time to peak | 2 h (range 1–3) | 0.5 h (range 0.08–1) |
| Mean AUC, 0–48 h | 54.6 h·ng/mL | 29.4 h·ng/mL |
| Half-life | About 3.4 h (oral dose in asthma patients) | 5.7 h mean terminal half-life (9 of 17 subjects) |
Other label points:
- Incomplete oral absorption. In a small study, only 30–50% of an oral dose was recovered in urine after 3 days, with the rest in feces, which may indicate poor absorption.
- Variable half-life after injection. In one study the half-life was about 2.9 h in 10 of 14 patients but 6–14 h in the other 4.
- Kidney elimination. About 90% of an injected dose is excreted in urine by 96 hours, about 60% of it unchanged. The sulfate conjugate is the main metabolite.
- Onset. After tablets, airflow changes within 30 minutes and peaks at 2–3 hours, with effects lasting 4 hours or longer. After injection, a clinically significant rise in FEV₁ (air blown out in one second) occurs within 15 minutes.
- Crosses the placenta. Umbilical blood levels were 11–48% of maternal levels after an IV dose in late pregnancy.
Inhaled terbutaline builds up with daily use. In 12 trained men inhaling 2 mg/day, peak serum levels were 6.4 ng/mL after 7 days versus 4.9 ng/mL after the first dose, and urine excretion was higher too (Krogh et al., Med Sci Sports Exerc 2017).
Approved medical use
Both US labels approve terbutaline for the prevention and reversal of bronchospasm in patients 12 years and older with asthma, and reversible bronchospasm with bronchitis and emphysema (tablet label; injection label).
| Form | Population | Labeled dose |
|---|---|---|
| Tablets | Adults | 5 mg about every 6 hours, three times daily while awake; may be reduced to 2.5 mg three times daily if side effects are troublesome; no more than 15 mg in 24 h |
| Tablets | Ages 12–15 | 2.5 mg three times daily; no more than 7.5 mg in 24 h |
| Tablets | Under 12 | Not recommended |
| Injection | Ages 12 and up | 0.25 mg subcutaneously in the lateral deltoid; a second 0.25 mg dose after 15–30 minutes if needed; no more than 0.5 mg in 4 h |
The injection is labeled for subcutaneous use only, not intravenous infusion. Both labels warn that needing more doses than usual can signal worsening asthma, and that beta-agonists alone may not control asthma without anti-inflammatory treatment such as corticosteroids.
Preterm labor: an unapproved use with a boxed warning
Terbutaline was long used off-label to delay preterm labor (tocolysis), including by oral tablets and by subcutaneous pump at home. On February 17, 2011, FDA announced a boxed warning and contraindication for both forms (FDA Drug Safety Communication, 2011; archived copy):
- Injection: should not be used for prevention or prolonged treatment (beyond 48–72 hours) of preterm labor, in hospital or outpatient settings.
- Tablets: should not be used for prevention or any treatment of preterm labor, because they have not been shown to work and carry similar safety concerns.
FDA’s review of its adverse event database found 16 maternal deaths reported from initial marketing in 1976 through 2009. It also found 12 serious maternal cardiovascular events reported from 1998 to July 2009, including arrhythmias, heart attack, pulmonary edema, high blood pressure and tachycardia. FDA concluded that the risks outweighed any potential benefit for prolonged injectable or any oral use in pregnancy.
Trials support the lack of benefit. A Cochrane review of 4 trials (234 women) found no evidence that terbutaline pump maintenance therapy improved newborn outcomes. Gestational age at birth differed by −0.14 weeks versus a saline pump (95% CI −1.66 to 1.38) (Chawanpaiboon et al., Cochrane 2014). A separate Cochrane review concluded that the evidence does not support oral betamimetics for maintenance therapy after threatened preterm labor (Dodd et al., Cochrane 2012).
What the research shows on muscle, fat and performance
Beta-2 agonists are anabolic in rodents, which is why they draw interest in bodybuilding (Jessen et al., Scand J Med Sci Sports 2018). The human evidence for terbutaline comes almost entirely from one research group at the University of Copenhagen. Their trials were small (9–67 participants), short (4 weeks), done in healthy young men, and mostly used inhaled terbutaline, which is not sold in the US. None was designed to test fat loss as a main goal.
Lean mass and body composition
| Trial | Design | Terbutaline dose | Result vs placebo |
|---|---|---|---|
| Hostrup et al., J Appl Physiol 2015 | RCT, 18 trained men, 4 weeks | Oral, 5 mg per 30 kg body weight twice daily | Lean mass +1.95 kg; quadriceps force +97 N; larger type I and type II muscle fibers |
| Jessen et al., Scand J Med Sci Sports 2018 | RCT, 67 men, 4 weeks, three training arms | Inhaled, 8 × 0.5 mg/day | Lean mass +1.03 kg (95% CI 0.29–1.76) without training; +1.04 kg (95% CI 0.16–1.93) with resistance training; no gain with endurance training. No change in fat mass or resting metabolic rate |
| Jessen et al., J Physiol 2022 | RCT, 21 healthy men, 4 weeks | Inhaled, 4 mg/day | Insulin-stimulated glucose disposal +27%; the change tracked the gain in lean mass |
Points to keep in mind:
- The oral dose in the 2015 trial was weight-based (5 mg per 30 kg, twice daily), while the US label sets a fixed maximum of 15 mg/day.
- The inhaled dose of 4 mg/day was described by the authors as “near-therapeutic.” It is still a daily dose in healthy people with no airway disease.
- No fat-loss effect was shown. In the largest trial, fat mass did not change differently from placebo.
- Only short-term data. The trials above lasted 4 weeks and did not report long-term muscle, heart or safety outcomes.
Strength and sprint performance
Single high doses improved short, maximal efforts in small crossover trials:
| Trial | n | Dose | Main result vs placebo |
|---|---|---|---|
| Hostrup et al., Eur J Appl Physiol 2014 | 9 trained men | Inhaled 15 mg (30 × 0.5 mg) | Quadriceps strength 738 vs 681 N; 30-s sprint peak power +2.2%, mean power +3.3%; no change in a 100-kcal time trial |
| Kalsen et al., Med Sci Sports Exerc 2016 | 9 moderately trained men | Inhaled 15 mg | 10-s sprint mean power +8.3%, peak power +7.8%; faster muscle glycogen breakdown |
| Sanchez et al., Eur J Appl Physiol 2013 | 7 competitive male athletes | Oral 8 mg | No gain in aerobic or sprint performance; maximal strength decreased; all participants had side effects such as tremor |
The 15 mg inhaled dose in these trials is far above the 4 mg/day used in the chronic studies. The authors called it “high-dose”; it produced plasma levels of about 23.6 ng/mL at 30 minutes. For comparison, the label reports a mean peak of 8.3 ng/mL after a 5 mg tablet.
Endurance performance
Terbutaline did not improve endurance in the trials reviewed here:
- Inhaled 2 mg or 4 mg did not change 3-km running time in 16 healthy men and women, although it did raise FEV₁ and post-race lactate (Molphy et al., Int J Sports Physiol Perform 2019).
- Inhaled 15 mg did not change a 300-kcal cycling time trial in 9 trained men, while it increased carbohydrate burning during submaximal exercise (Kalsen et al., J Appl Physiol 2014).
- In 21 trained men doing 4 weeks of high-intensity training, adding daily inhaled terbutaline reduced the performance gain (6.1% vs 11.6% without it). It also blunted gains in maximal oxygen uptake (VO₂max) and shifted muscle toward a fast-twitch profile (Hostrup et al., J Physiol 2018).
- With 4 weeks of inhaled terbutaline, VO₂max relative to body mass fell compared with placebo, and muscle content of mitochondrial respiratory-chain proteins dropped by 11% (Lemminger et al., Scand J Med Sci Sports 2019).
What the meta-analyses say for beta-2 agonists as a class
Two 2020–2021 meta-analyses pooled randomized trials of beta-2 agonists in healthy, non-asthmatic people:
| Outcome | Studies | Pooled result |
|---|---|---|
| Strength, sprint and power (efforts of 1 minute or less) | 34 studies | Improved by about 5% (standardized difference 0.29, 95% CI 0.16–0.42); larger with oral, prohibited or multi-week use |
| Aerobic performance (efforts over 1 minute) | 47 studies | No effect (standardized difference 0.051, 95% CI −0.020 to 0.122) |
Sources: Riiser et al., Br J Sports Med 2020; Riiser et al., Br J Sports Med 2021. The first review noted that it is uncertain whether doses WADA allows improve performance.
Side effects and risks
Boxed warning: tocolysis
The tablet label states that oral terbutaline has not been approved and should not be used for acute or maintenance tocolysis. The injection label states that it should not be used for prolonged tocolysis beyond 48–72 hours. Both list the same serious reactions reported in pregnant women (tablet label; injection label):
- in the mother: fast heart rate, temporary high blood sugar, low potassium, arrhythmias, pulmonary edema (fluid in the lungs), myocardial ischemia (reduced blood flow to the heart muscle), and death;
- in the baby: faster fetal heart rate and low blood sugar after birth.
Heart and blood vessels
The labels warn that terbutaline, like all beta-agonists, can produce clinically significant changes in pulse, blood pressure or symptoms. Beta-agonists have been reported to cause ECG changes, including T-wave flattening, QTc prolongation and ST depression. The labels advise caution in people with coronary insufficiency, arrhythmias, hypertension, hyperthyroidism, diabetes or seizure disorders. Rare seizures have also been reported.
In laboratory animals (minipigs, rodents and dogs), beta-agonists given together with methylxanthines such as theophylline caused arrhythmias and sudden death with heart muscle damage. The clinical relevance in people is unknown, per the labels.
Across the beta-2 agonist class, a meta-analysis of placebo-controlled trials in asthma and COPD found that a single dose raised heart rate by 9.12 beats/min and lowered potassium by 0.36 mmol/L. In trials lasting 3 days to 1 year, beta-2 agonists increased the risk of a cardiovascular event (RR 2.54, 95% CI 1.59–4.05), driven mainly by sinus tachycardia (Salpeter et al., Chest 2004). These are class data, not terbutaline-specific.
Potassium, blood sugar and overdose
- Low potassium (hypokalemia). Beta-agonists can cause significant hypokalemia by shifting potassium into cells, which can harm the heart. It is usually temporary.
- Blood sugar. Large IV doses have worsened diabetes and ketoacidosis.
- Overdose. Expected signs include seizures, angina, high or low blood pressure, heart rates up to 200 beats/min, arrhythmias, tremor and hypokalemia. There is no specific antidote.
Common side effects (label rates)
| Reaction | Tablets, 5–15 mg/day (n = 199) | Injection 0.25 mg (n = 77) | Injection 0.5 mg (n = 205) |
|---|---|---|---|
| Nervousness | 35.0% | 16.9% | 30.7% |
| Tremor | 15.0% | 7.8% | 38% |
| Headache | 7.5% | 7.8% | 8.8% |
| Palpitations | 5.0% | 7.8% | 22.9% |
| Drowsiness / somnolence | 5.5% | 11.7% | 9.8% |
| Dizziness | 3.5% | 1.3% | 10.2% |
| Tachycardia | 3.5% | 1.3% | 1.5% |
| Nausea (vomiting) | 3.0% | 1.3% | 3.9% |
The tablet label reports that these effects tend to lessen with continued use. Rare liver enzyme elevations and hypersensitivity vasculitis have also been reported.
Interactions
The labels list these interactions:
- Other sympathomimetics (stimulant-type drugs acting on adrenaline receptors): combined use is not recommended because of additive heart effects.
- MAO inhibitors and tricyclic antidepressants: use only with extreme caution, including within 2 weeks of stopping them, because vascular effects may be potentiated.
- Beta-blockers: block terbutaline’s effect and can cause severe bronchospasm in people with asthma.
- Loop and thiazide diuretics: ECG changes and low potassium can be acutely worsened, especially above the recommended beta-agonist dose.
Who should not use it
The labels contraindicate terbutaline for tocolysis as described above and in people hypersensitive to sympathomimetic amines. It is not recommended under age 12. The labels also report animal findings: offspring of rats given terbutaline late in pregnancy showed changes in behavior and brain development, and rats fed high doses for 2 years developed benign tumors of the mesovarium (the tissue that supports the ovary).
Legal status and use in sport
United States. Terbutaline tablets and injection are prescription-only drugs. No inhaled terbutaline product is currently marketed in the US.
WADA. The WADA 2026 Prohibited List names terbutaline under S3 beta-2 agonists, which are prohibited at all times, in and out of competition. All substances in S3 are “Specified Substances” under WADA rules. The list exempts inhaled salbutamol, formoterol, salmeterol and vilanterol up to set doses, but terbutaline has no exception by any route. An athlete with asthma who needs it therefore requires a Therapeutic Use Exemption (TUE).
Key takeaways
- An approved asthma drug, not a steroid. US labels cover oral tablets (up to 15 mg/day) and subcutaneous injection for bronchospasm in people 12 and older.
- A boxed warning for pregnancy. Since 2011, FDA has warned against prolonged injectable or any oral use for preterm labor, after reports of 16 maternal deaths and serious heart events.
- Some muscle growth in small trials. Four-week trials in healthy young men found about 1–2 kg more lean mass than placebo. Fat mass did not fall, and no long-term data exist.
- Sprint power, not endurance. High single doses raised sprint power and strength in some small trials. Endurance did not improve, and daily use blunted gains from interval training.
- Heart and potassium effects are the main risks. Tremor, nervousness and palpitations are common; tachycardia, arrhythmias, ECG changes and low potassium are the serious concerns.
- Banned in sport at all times. WADA’s 2026 list prohibits terbutaline under S3 with no inhaled-dose exception, so athletes need a TUE.
Sources
- Chartwell RX. Terbutaline sulfate tablets, USP, prescribing information (revised 02/2023). DailyMed.
- Fresenius Kabi USA. Terbutaline sulfate injection, USP, prescribing information (revised 04/2022). DailyMed.
- Food and Drug Administration. FDA Drug Safety Communication: New warnings against use of terbutaline to treat preterm labor. February 17, 2011. FDA; archived copy.
- Food and Drug Administration. Drugs@FDA: Brethine, NDA 017849; Bricanyl injection, NDA 017466; Bricanyl tablets, NDA 017618; Brethaire, NDA 018762; Bricanyl aerosol, NDA 018000. NDA 017849; NDA 017466; NDA 017618; NDA 018762; NDA 018000.
- National Center for Biotechnology Information. PubChem Compound Summary for CID 5403, Terbutaline. PubChem.
- World Anti-Doping Agency. 2026 Prohibited List. In effect from January 1, 2026. WADA.
- Krogh N, Rzeppa S, Dyreborg A, et al. Terbutaline accumulates in blood and urine after daily therapeutic inhalation. Med Sci Sports Exerc. 2017;49(6):1236–1243. PubMed.
- Chawanpaiboon S, Laopaiboon M, Lumbiganon P, et al. Terbutaline pump maintenance therapy after threatened preterm labour for reducing adverse neonatal outcomes. Cochrane Database Syst Rev. 2014;2014(3):CD010800. PubMed.
- Dodd JM, Crowther CA, Middleton P. Oral betamimetics for maintenance therapy after threatened preterm labour. Cochrane Database Syst Rev. 2012;12(12):CD003927. PubMed.
- Hostrup M, Kalsen A, Onslev J, et al. Mechanisms underlying enhancements in muscle force and power output during maximal cycle ergometer exercise induced by chronic β2-adrenergic stimulation in men. J Appl Physiol. 2015;119(5):475–486. PubMed.
- Jessen S, Onslev J, Lemminger A, et al. Hypertrophic effect of inhaled beta2-agonist with and without concurrent exercise training: a randomized controlled trial. Scand J Med Sci Sports. 2018;28(10):2114–2122. PubMed.
- Jessen S, Baasch-Skytte T, Onslev J, et al. Muscle hypertrophic effect of inhaled beta2-agonist is associated with augmented insulin-stimulated whole-body glucose disposal in young men. J Physiol. 2022;600(10):2345–2357. PubMed.
- Hostrup M, Kalsen A, Bangsbo J, et al. High-dose inhaled terbutaline increases muscle strength and enhances maximal sprint performance in trained men. Eur J Appl Physiol. 2014;114(12):2499–2508. PubMed.
- Kalsen A, Hostrup M, Söderlund K, et al. Inhaled beta2-agonist increases power output and glycolysis during sprinting in men. Med Sci Sports Exerc. 2016;48(1):39–48. PubMed.
- Sanchez AM, Borrani F, Le Fur MA, et al. Acute supra-therapeutic oral terbutaline administration has no ergogenic effect in non-asthmatic athletes. Eur J Appl Physiol. 2013;113(2):411–418. PubMed.
- Molphy J, Dickinson JW, Chester NJ, et al. The effects of inhaled terbutaline on 3-km running time-trial performance. Int J Sports Physiol Perform. 2019;14(6):822–828. PubMed.
- Kalsen A, Hostrup M, Karlsson S, et al. Effect of inhaled terbutaline on substrate utilization and 300-kcal time trial performance. J Appl Physiol. 2014;117(10):1180–1187. PubMed.
- Hostrup M, Onslev J, Jacobson GA, et al. Chronic β2-adrenoceptor agonist treatment alters muscle proteome and functional adaptations induced by high intensity training in young men. J Physiol. 2018;596(2):231–252. PubMed.
- Lemminger AK, Jessen S, Habib S, et al. Effect of beta2-adrenergic agonist and resistance training on maximal oxygen uptake and muscle oxidative enzymes in men. Scand J Med Sci Sports. 2019;29(12):1881–1891. PubMed.
- Riiser A, Stensrud T, Stang J, et al. Can β2-agonists have an ergogenic effect on strength, sprint or power performance? Systematic review and meta-analysis of RCTs. Br J Sports Med. 2020;54(22):1351–1359. PubMed.
- Riiser A, Stensrud T, Stang J, et al. Aerobic performance among healthy (non-asthmatic) adults using beta2-agonists: a systematic review and meta-analysis of randomised controlled trials. Br J Sports Med. 2021;55(17):975–983. PubMed.
- Salpeter SR, Ormiston TM, Salpeter EE. Cardiovascular effects of beta-agonists in patients with asthma and COPD: a meta-analysis. Chest. 2004;125(6):2309–2321. PubMed.