The project's primary purpose is to test the hypothesis that oral administration of a low single dose of β-antagonist propranolol (40 mg) reduces pain sensitivity in patients with masticatory muscle pain.

Inclusion Criteria:

• Meet Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) for myofascial TMD diagnosis corresponding to group 1a or 1b
• Characteristic Pain Intensity (CPI) more than or equal to 20 (Axe II, RDC/TMD questionnaire)
• Women of childbearing potential must use adequate contraception
• Signed consent statement

Exclusion Criteria:

• Other acute pain cause such as acute toothache or a pain condition the investigator estimates to be contraindicated for participation in the experiment
• Recognized existing malignancy or within last 5 years
• Known HIV
• Abuse of drugs including alcohol
• Recognized Raynaud's syndrome
• Former sympathectomy
• Known cardiovascular disease including abnormal EKG and blood pressure (ECG-12 is recorded before the first trial session and assessed by the physician)
• Recognized lung insufficience, including bronchial asthma
• Known severe hepatic or renal dysfunction
• Known diabetes mellitus
• Known severe depression
• Pregnancy (tests performed in both sessions 1 and 2 before the start of a session)
• Fertility Treatment
• Lactation
• Post-menopausal
• Previous adverse reaction when taking beta-blocker, including hypersensitivity to propranolol or to any of the excipients
• Patients who can not read and understand the written information
• Patients who can not follow the protocol
• Patients who do not agree to comply with the requirements for participation in both studies regarding food intake, physical activity, etc.