Yes it is possible to fail a Class 1 medical examination but it depends entirely on your health status and whether you meet the aviation medical standards set by the regulatory authority (DGCA in India FAA in the U.S. or ICAO based standards).
Medical disqualifications: If you have certain serious or uncontrolled medical conditions such as uncontrolled hypertension significant cardiac abnormalities, severe pulmonary dysfunction, serious untreated ENT issues or disqualifying mental health diagnoses the examiner may refuse to issue the Class 1 certificate.
Poor documentation or incomplete testing: If required tests (ECG ECHO pulmonary function blood and urine lab work, hearing and vision assessments psychological screening etc.) are missing or inconclusive, the medical board might withhold certification or ask for further investigation.
Vision or hearing deficiencies that aren’t correctable: If your eyesight, even with corrective lenses, doesn’t meet the specified aviation standards (for example FAA standards require 20/20 distant vision or 20/40 near, and acceptable hearing), you might be deemed unfit until those issues are resolved.
The goal of a Class 1 medical isn’t to “catch people out” but to ensure safety in commercial aviation. The standards are strict, but many potential problems can be mitigated or corrected.
Many candidates who initially do not meet the criteria are able to address the medical issues through treatment lifestyle changes or corrective aids (e.g.glasses medication follow up cardiology care). If health issues are stabilized and evidence of recovery or control is provided certification may be granted.
Medical examiners often try to find a path to certification rather than immediate rejection. If a candidate has a condition that might be manageable the examiner or medical board may require further testing follow up care or temporary restrictions rather than a blanket fail.