[4] Common side effects include nausea, diarrhea, abdominal pain, and loss of appetite.

[6] Ethionamide is used in combination with other antituberculosis agents as part of a second-line regimen for active tuberculosis.

[8][9] It crosses the blood brain barrier to achieve concentrations in the cerebral-spinal fluid equivalent to plasma.

[7] While working in a similar manner to isoniazid, cross resistance is only seen in 13% of strains, since they are both prodrugs but activated by different pathways.

[7] Ethionamide frequently causes gastrointestinal distress with nausea and vomiting which can lead patients to stop taking it.

[15] Both central neurological side effects such as psychiatric disturbances and encephalopathy, along with peripheral neuropathy have been reported.

[7] Ethionamide is structurally similar to methimazole, which is used to inhibit thyroid hormone synthesis, and has been linked to hypothyroidism in several TB patients.

[1] Ethionamide is a prodrug[17] which is activated by the enzyme ethA, a mono-oxygenase in Mycobacterium tuberculosis, and then binds NAD+ to form an adduct which inhibits InhA in the same way as isoniazid.

It is thought that improving ethA expression will increase the efficacy of ethionamide and prompting interest by drug developers in EthR inhibitors as a co-drug.