Asthma, a common chronic inflammatory disease of the airways, causes wheezing, coughing, chest tightness, and shortness of breath. Carvacrol is the main phenol of the essential oil of plants including oregano (Origanum vulgare, Lamiaceae) and thyme (Thymus vulgaris, Lamiaceae), and has been shown to have antioxidant and anti-inflammatory effects. These authors conducted a randomized, double-blind, placebo-controlled, phase II clinical trial to evaluate carvacrol’s effects on pulmonary function test (PFT) values, respiratory symptoms, and lung inflammation in patients with asthma.
Patients aged 20 to 70 years with moderate to severe asthma were recruited from the asthma clinic at Mashhad University of Medical Sciences in Mashhad, Iran [dates not given]. All patients had two or more of the following symptoms: cough or chest tightness at rest; nocturnal or early morning wheezing, coughing, or chest tightness; and wheezing or coughing during exercise. Their forced expiratory volume in the first second and peak expiratory flow (PEF) was less than 80% of predicted values. Exclusion criteria included other chronic diseases, current respiratory infection, and pregnancy.
Patients were randomly assigned to take placebo or carvacrol capsules for two months while continuing to use previously prescribed treatment. Pharmaceutical grade (90%) carvacrol was purchased from Ji’An HaiRui Natural Plant Company in China and used to prepare coated pellets used to make 30 mg carvacrol capsules used in the study. The placebo capsules were not described. Because prior animal studies suggested that a suitable daily dose of carvacrol was about 1.2 mg/kg, patients weighing up to 60 kg were given two capsules per day, and those over 60 kg were given three.
Pulmonary function and respiratory symptoms were evaluated and blood samples were drawn at baseline, after one month of treatment, and at the end of the study. Blood tests included complete blood cell counts and high-sensitivity C-reactive protein (hs-CRP), a biomarker for chronic inflammation.
Twenty-eight patients were recruited, with 14 each assigned to the carvacrol and placebo groups. During the study, two patients in the carvacrol group and three in the placebo group discontinued the intervention and were not included in the final analyses. At baseline, 54.5% of the four males and seven females in the placebo group had a family history of asthma, and 27% had a history of passive smoking. In the carvacrol group, 66.7% of the four males and eight females had a family history of asthma, and 50% had a history of passive smoking. The carvacrol group had nonsignificantly greater severity of asthma according to a scoring scale that was not explained in the paper.
In the placebo group, maximum expiratory flow at 75% (MEF75) and at 50% (MEF50) of the vital capacity during a forced expiration decreased at the end of the study compared with baseline (P<0.01 and P<0.05, respectively), and MEF75 decreased at the end of the study compared with the end of month one (P<0.01). In the carvacrol group, by contrast, MEF at 25%-75% was significantly increased (all P<0.05 after one month, P<0.001 at the end of the study). Additionally, significant increases were seen in forced vital capacity (FVC), peak expiratory flow (PEF), and maximum mid-expiratory flow (MMEF) percentages compared with baseline (all P<0.001 after two months). Final differences between the groups significantly favored the carvacrol group (P<0.001 for MEF75, MVF50, and FVC; P<0.01 for MMEF; P<0.05 for PEF).
Daytime wheezing decreased in the carvacrol group after one month (P<0.01) and after two months (P<0.001) compared with baseline, and those decreases were greater than those in the placebo group after one month (P<0.05) and after two months (P<0.01). The carvacrol group experienced decreased wheezing during exercise (P<0.05 after one month, P<0.01 after two months), significantly better than the placebo group (after two months, P<0.01 and P<0.001 respectively).
Serum hs-CRP levels significantly decreased in the carvacrol group at the end of the study compared with baseline (P<0.001). There was no decrease in the placebo group, and the final between-group difference was significant (P<0.05). Changes in blood cell counts were all small, though sometimes statistically significant. No adverse effects were reported during the study.
Limitations of this study include the relatively short duration and the small sample size. Additionally, the effects of lower and higher doses of carvacrol on patients with different severities of asthma would need to be evaluated. “These results indicate possible preventive therapeutic effects of carvacrol on respiratory symptoms and PFT values in asthma,” the authors concluded.
The authors declared no conflicts of interest.
Alavinezhad A, Khazdair MR, Boskabady MH. The possible therapeutic effect of carvacrol on asthmatic patients: a randomized, double-blind, placebo-controlled, Phase II clinical trial. Phytother Res. January 2018;32(1):151-159. doi: 10.1002/ptr.5967.