Psychosis
Isotretinoin has also been linked to psychosis. Many of the side effects of isotretinoin mimic hypervitaminosis A, which has been associated with psychotic symptoms. The dopamine hypothesis of schizophrenia and psychosis suggests that an increase in dopaminergic stimulation or sensitivity in the limbic system causes psychotic symptoms.It has been suggested that dysregulation of retinoid receptors by retinoids such as isotretinoin may cause schizophrenia. The evidence for this is threefold: transcriptional activation of the dopamine D2 receptor – in addition to serotonin and glutamate receptors – is regulated by retinoic acid; schizophrenia and the retinoid cascade have been linked to the same gene loci; and retinoid dysfunction causes congenital anomalies identical to those observed in people with schizophrenia. Further, the expression of dopamine receptors has indeed been shown to be regulated by retinoic acid. Musculoskeletal
Isotretinoin has a number of muscoloskeletal effects. Myalgia (muscular pain) and arthralgia (joint pain) are rare side effects. Retinoids, such as high dose etretinate, are well known to cause bone changes, the most common type of which is hyperostotic changes (excessive bone growth), especially in growing children and adolescents. Other problems include premature epiphyseal closure and calcification of tendons and ligaments. The bones of the spine and feet are most commonly affected. Risk factors for skeletal effects include older age, greater dosage and longer course of treatment. Most bone changes cause no symptoms and may only be noticed using X-ray imaging. Gastrointestinal
Isotretinoin may cause non-specific gastrointestinal symptoms including nausea, diarrhea and abdominal pain.
Bacterial colonization: Poor oral hygiene can result in colonization of the mouth with excessive amounts of bacteria, which is linked to increased incidence of aspiration pneumonia. Ethnicity: Asians diagnosed with aspiration pneumonia have a lower risk of death compared to other ethnic groups while African Americans and whites share a relatively similar risk of death. Hispanics have a lower risk of death than non-Hispanics. Others: Age, male gender, diabetes mellitus, malnutrition, use of antipsychotic drugs, proton pump inhibitors, and angiotensin-converting enzyme inhibitors. Residence in an institutional setting, prolonged hospitalization or surgical procedures, gastric tube feeding, mechanical airway interventions, immunocompromised, history of smoking, antibiotic therapy, advanced age, reduced pulmonary clearance, diminished cough reflex, disrupted normal mucosal barrier, impaired mucociliary clearance, alter cellular and humoral immunity, obstruction of the airways, and damaged lung tissue. Bacteria
Bacteria involved in aspiration pneumonia may be either aerobic or anaerobic. Common aerobic bacteria involved include:

Streptococcus pneumoniae
Staphylococcus aureus
Haemophilus influenzae
Pseudomonas aeruginosa
Klebsiella: often seen in aspiration lobar pneumonia in alcoholicsAnaerobic bacteria also play a key role in the pathogenesis of aspiration pneumonia. They make up the majority of normal oral flora and the presence of putrid fluid in the lungs is highly suggestive of aspiration pneumonia secondary to an anaerobic organism. While it is difficult to confirm the presence of anaerobes through cultures, the treatment of aspiration pneumonia typically includes anaerobic coverage regardless. Potential anaerobic bacteria are as follows:

Bacteroides
Prevotella
Fusobacterium
Peptostreptococcus

Pathophysiology
Aspiration is defined as inhalation of oropharyngeal or gastric contents into the pulmonary tree.